OK I filled out your supermassive form. Let's click ‘Submit’ and… whuh? Where'd it all go?

I keep flushing but it won't go down.

Apologies for the unpleasantness but a resilient floater was not what I expected to find in a restroom of a bright, clean and as-yet sparsely occupied café this morning. Everything looked so welcoming and breezy when arrived, I would never have imagined such an establishment would house a dimly lit, evil-smelling black hole of human waste behind the door marked "W.C."

Talk about mixed messaging.

Out front, the café was gently buzzing with light chatter, the tinkling of spoons on ceramic and gentle acoustic indie folk music. In the back, it is all dank dripping and gurgling pipes, and I think I can hear the tormented moans of outcast souls punctuating the discordant warble of the overture to The Phantom of the Opera. I fully expect this to be joined by the buzzing of flies and an evil voice grunting "GET OUT!"

I comply and stumble out of the cubicle bathed in cold sweat, frantically cleansing my hands with anti-bacterial gel up to the elbows.

Back in the café's main area, I am in another world. A fresh-faced young woman carrying a tray gives me a sweet smile and invites me to order my drinks at the cash till. Joni Mitchell is now playing on the hi-fi and the room smells faintly of joss-sticks. What a relief! This is a nice place after all! I consult the price list on the wall, cheerfully ask for a coffee… and only then do I turn to the man taking my order.

He stands there facing me, immobile, stony faced. He is wearing a t-shirt bearing a slogan that reads, in huge letters, "FUCK OFF".

The anti-logic is impeccable. It is akin to Matthew Modine's character in Full Metal Jacket trying to explain that wearing a Peace symbol button on his shirt while the words "Born to kill" are scrawled on his helmet are supposed to suggest "something to do with the duality of Man."

Deep, huh? I'm not sure where the comedy turd* comes in but then Philosophy wasn't on the curriculum when I went through the British school system.

Similar conflicting forces come into play when I try to settle the bill. The waitress declined my cash, saying she had run short of change, and she asks me to pay by card at the desk. I head back to the till but when I present my card to the machine, it flashes up a message "Waiting…" with animated dots and remains like this for a minute as my contactless code spirals into a black hole of 4G nothingness. "Oh yes," says Monsieur FUCK OFF, "the machine isn't working today."

So you won't take cash and can't accept card payment, I observe. How would you like me to pay for my coffee? An IOU? Some kind of barter system? I might have a few ballpoint pens in my bag. If I'd known, I would have brought a cow with me.

They hadn't thought of this. More inconsistent messaging. Mr FO, the waitress and I look at each other, each waiting for a solution from heaven. Rather, I suspect we will all soon be sucked into that same black hole as my card details to keep them company in the darkness where there is no more coffee and definitely no Joni Mitchell.

Just so you know, black holes actually sound like this, according to NASA's Marshall Space Flight Center.

Later in the afternoon, I go through the post and find a reminder that one of my British magazine subscriptions is due for renewal. The letter – which I am about to learn was written by a barefaced liar – assures me I can do this online.

The online renewal form can only be accessed once I enter my surname, subscriber number and postcode. Next to the postcode field is a tiny instruction that says it is not necessary to type anything here if I live outside the UK. I do so I don't.

But when I click the 'Find details' button, a red message appears just above the instruction. This says I must enter my postcode or, if I don't have one, enter 'NONE'. That is to say, there are now two contradictory instructions on-screen next to the postcode field: one is telling me to enter my postcode, the other tells me not to enter my postcode. Mixed messaging at its purest.

Typing 'NONE' into the field makes no difference. Nor does putting my actual postcode in there. Nor does typing 'POSTCODE', 'ABC123' or 'LET ME IN YOU DICKHEADS'.

How hard can it be to code a three-field form correctly? Well, maybe I'm just unlucky but I get this a lot.

From forms that do nothing when you click on the 'Submit' button – typically because it was coded to work exclusively with the coder's favourite web browser – to those that just act the fool, I seem to stumble across them all. I have reached a stage when I refuse to complete any long form with lots of fields because I just know that when I hit 'Submit', it will claim something isn't right, clear out every single field and insist that I enter them all over again.

Usually, problems arise from how the form builder chooses to restrict data types for each field. Nobody wants to sift through heaps of freeform text data when it arrives in the database, so it makes sense not to allow alphabetic characters in phone number fields or emojis in street names. But frequently I find I cannot enter my phone number at all because the form refuses to accept that a phone number could begin with two zeroes, and using a '+' sign is ruled out for being an illegal character. And don't get me started on postcodes – again.

From time to time, I still come across forms that refuse to acknowledge my email address is an email address. After investigating this issue, it turns out the problem is that my name is too short. The coder unilaterally decided that everybody in the world with fewer than four characters before the '@' sign should be shunned. If you're called Jon, Guy or indeed Ali, they would prefer you to sod right off.

Registering a password can be fun too. I used to come across 'New password' fields that required you to include a certain number of characters but didn't bother to tell you this. You end up trying one new password after another thinking there is a problem with your keyboard but actually all it wanted was between 12 and 20 characters: if you choose a password of 11 or 21 characters, it would blithely ask you to try again without explaining why.

These days it's much more common to see an instruction telling you to include "at least one special character" and then refuses to accept your password because you have wilfully typed in some special characters. Your fault is in not using the right special characters.

Secretly, the form coder has decided not only which is their favourite browser but they have favourite special characters too, and it is up to you to guess what they are. For them, form design is a thrilling bullet-train journey of self-expression; for you, it's a tiresome carthorse trot along a dirt track scattered with potholes. Yes, you can use hyphens and pluses; no you can't use ™ or ‡ or ÷ or ‰ or . I have found registration systems that refused to accept @, & or %. Oh they're just toooooo special!

My current contract involves helping customers register themselves with an examination provider whose registration form has been designed so that users' cursors cannot escape the Date of Birth field. Even the slightest nudge of a mouse scrollwheel just before they click 'Submit' is enough to cause the system to think they were – literally – born yesterday.

Don't tell anyone but I got a bit fed up with an official identification form issued as a PDF from the French Government and retagged it myself so that it worked properly.

It was bugging me that when I entered extended family details, the form copied this text into a number of irrelevant fields on a previous page, obliterating what I had already typed into them. It's a good job I spotted this otherwise it might have taken a bit of explaining to immigration officials why I had declared that my wife's middle names are 'Horace' and 'Horace' respectively and that I have 'Horace' nationality, having been born in a town called 'Horace' on the '9th of Horace'.

Looking at the form in Acrobat revealed the horror of what the form designer had done: they'd obviously copied and pasted fields from one place to another without bothering to relabel them internally, or indeed look at them at all. About a quarter of the fields were tagged, identically, with the helpful name 'text_19'.

Well, if the form designers can't be arsed to do the job without contradicting their own form rules – I say "can't be arsed" because form coding is about as simple a tagging task as you will ever get – what choice do I have? If you hear that I got deported, you'll know why.

In which case, I might end up along with my contactless code and countless other "invalid" and "illegal" form field text that I have typed over the years that were spirited away to the swirling black hole of form design incompetence. And it's a big one.

P.S. I paid the café bill to Monsieur FUCK OFF's email address via PayPal.