I used a diplomacy roll instead of seduction. The result of failure was that I've got a weird stare.

on thing to do for seduction failure is you succeed but the person is a yandere.

We tend to get that for succeeding on Charm rolls too well.
On the plus side, having an Inquisitor with a massive girlcrush on our Sororitas makes requisitioning support assets much easier.

I once offered to teach a merchant how to dance if I could get a discount. I didn't crit fail, but I rolled really low, so he said "no thanks, I uh, already have a wife, sir..."

Most of the time, in my groups, failed diplomacy checks mean that whatever silly nonsense the PC was spewing was thoroughly disbelieved.

The end result tends to be the PC confidently saying some obvious lie, while the NPC looks at them like they can't tell if they deserve to be locked up in jail or an asylum.

Most of the times when my players failed a check like diplomacy or subterfuge, I had the NPCs simply believe what the players were saying, not what their characters did.

So the opponents rightly assumed the characters were too weak to fight them, and not that they had a common cause.

the most interesting result we have had so far is a character botching a roll where they were passing on important information so what happened is that the NPC that was going to help them instead ran off somewhere else because the character got slightly confused and stumbled over their words. the end result was a very hard fight that would have been easier with help but of course something had to go wrong

Failed a diplomancy check. Rather than understand the evacuation, the queen thought I was putting the moves on her.

Normally, I'd assume that someone completely misinterpreted the words said to get that kind of misunderstanding, but based on what I've seen from you, the words were probably somehow pretty similar.

"Your highness! I have to get you out of the castle! Quickly, we must hurry before the King arrives!"

I was referring to the enemy king, leading the invasion. She didn't know the castle was being attacked.

I cannot remember any diplomacy roles, but I had a character with fencing where when I botched the roll the gm sometimes had me outright kill the opponent.

So the context was we were playing sorcerers crusade, 1500s europe. A bit freeform but still with character sheets.

While playing my character got ridiculously specced towards fencing, like five dex, five in melee, speciality in fencing(and the speciality used dots and they were maxed out), special high quality sword, I think it was magic or some shit, anyhow.

Once while trying to disarm (and intending to talk down) a guard I bothched and stabbed him to dead. We were in like Beijing, had to run from the city after that.

In India I tried to take a fleeing merchant that had fleeced us alive, botched, he broke his neck. Couldn't return or gods or get back our money after that.

Back in germany we were waylaying a princess and her fiancee. Since I was good at fencing I reached the carriage first, the fiance tried to stab me, since we wanted the important noble people alive as hostages I tried to disarm him, botched, stabbed him in the gut and he bled out in front of me. Princess became hysteric and I had to try and calm her down while the rest of the group actually participated in the combat.

That last one seems like a missed opportunity; I'd have gone with 'You have successfull disarmed him. He is now in immediate danger of dying of massive blood-loss from the brachial artery.'

well, not diplomacy, but intimidation.

one of my players tried to intimidate the mall cop to leave them alone so they could stalk and set up an ambush, and fumbled.

he got the guards phone number, a squeezed buttock, and a sweet, soft whisper "i get of at 4..." in his ear...

but hey, they were left alone to shadow and ambush that business dude, soo, success?

Once failed a dyplomacy roll on a NPC who hated us already, when trying to convince her that we could be trusted and knew our buisness about adventureing.
She stopped hating us and started looking down on us, like "how pittyful. You should stop traveling this world is too dangerous for you."
we never managed to convince her otherwhise.