I went to Paris for Valentines Day many moons ago. The restaurant we had dinner in that night was, understandably, very busy and we were seated very close to an American couple, who loudly started complaining to each other about us being so close to them.
They ordered the most expensive thing on the quite swanky menu - a large joint of beef for two - which was served with a flourish and carved at the table. They complained it was too rare and sent it back. The waitress replaced it without a word.
They had to wait a while for the replacement, and they were drinking the whole time, and getting more vociferous in their complaints - just passive aggressively to each other but in everyone's hearing. We started loudly and exaggeratedly discussing the deliciousness of our food, just for funsies.
They ate the second joint of meat, whilst loudly complaining about its shoe leather texture and how it had been clearly microwaved, but when the bill came they refused to pay for it (they were only charged for one joint). The manager came over and politely told them they would have to pay for what they had eaten.
They became even more unreasonable, refusing to pay for the wine because they'd only ordered it whilst waiting so long for their replacement mains (wtf?). The woman started screeching for their coats (which were in a cloakroom separate from the restaurant) but he manager held his ground, saying they couldn't leave until they had paid the bill.
She heard us making sarcastic comments and came over and hissed at my then-boyfriend "you have a tiny dick. Your wife told me". Wowsers.
It culminated in the woman trying to push past a waiter to get to her coat, screeching all the while. He tried to stop her going through the doorway....so she bit him! Then, whilst he recoiled, her husband punched him in the face and the waiter punched him back! She ran screaming into the street for the police, who arrived in a few minutes. Shortly after they were meekly paying their bill, accompanied by a burly French police officer.