Mine pales in comparison to most of these, as I have never had the chance to travel overseas, but anywho…
My BFF and I have had many an encounter with random fast food managers, she is very vocal about the ordering, preparation, serving of her food. I can’t tell you how many free meals we have gotten. This particular time we were at a Pizza Hut, we ordered our medium pepperoni pizza and bread sticks. We waited, and waited, finally our order arrives, and it is a large supreme. So we inform the waitress, who proceeds to sit down in the both next to me, shoving my jacket onto the floor, and tells us how we are both wrong and we should never question the person holding the receipt. 
The receipt said a medium pepperoni. Fortunately, I was friends with that particular manager and called her out front, and we ended up having a good laugh about it. Apparently that waitress had a previous meltdown the day before about drink refills. I never saw her there again, and we got that meal for free, but we still laugh about it every time we eat there.
I was eating dinner with several friends at a Don Pablos, and two of them are picky eaters, and always tack half a dozen requests onto their food. The food arrived, wheeled up on a cart by a very large black man in an apron. He looked like he would have been passed over as an NFL linebacker for being too big and rough looking. As he passed the food out, it was checked for correctness, and one of my friends saw that they didn’t put any X on her food, like she asked. She said ‘Excuse me, I asked for X on my food.’ This guys didn’t even pause, he reached into his apron, pulled out the order receipt, held it up and bellowed ‘Do you see this?’ The rest of us saw the grin on his face, and realized he was joking, but she did not. She went white as a sheet and backed into the corner of the booth. When he saw this he immediately stopped and made it obvious he was joking. He took her food back and got some X on it. We still joke with her about it.
Another time, same friends plus a few, same restaurant. The waiter goes around the table taking orders. When he finishes, he says ‘If you have any questions, let me know.’ I look up and ask ‘What’s the capital of South Dakota?’ He gets a blank look on his face and says that he’s not sure, and walks away. A few minutes later, he comes back and asks me if it’s Pierre. I reply that I did not know, hence the asking. He walks away again. A few minutes later a different waitress walks up and says she thinks it’s Bismark. Again, I reply that I did not know the answer. The rest of the evening, we are approached by 6 different people with guesses, including the hostess. As we’re settling the check, an important looking person with ‘Manger’ on her name tag walks up, and gruffly demands to know who asked the question. I slowly raise my hand. She stares at me for a second and says ‘It’s Pierre’. And walks away. I am henceforth forbidden to ask questions in restaurants.
My mother and I were in Penang and found a funny little concrete building (looked like a public toilet block from the outside) where all the locals ate.
It had maybe 20 small stalls inside and we ordered at a place that had half chickens grilling (so gooood, came with a soup and rice and was about 50 cents).
So we’re sitting down and tucking in to our lovely meal when the guy behind the counter comes to sit with us at our table and starts flirting with me.
We are both being quite polite but short enough with him that you’d think he’d get the message.
He suddenly pops out with,
“You sralians! Where you from in stralia!? My sister in stralia!”
Grabs his mobile phone out and dials his sister who has just moved to Sydney and insists that we must speak with her.
My mother spends 15 minutes on the phone to his sister who had worked in the little food court in Penang. It was rather bizarre travelling to another country to call someone you’d never met back home.
Bizarre but quite nice 
Wow, we didn’t know. My husband is a grad student at Rutgers but we’ve only lived here for 2 months. Maybe some day we’ll get brave enough to try something off the… uhm… grease truck. 
We went to Pizza Hut once on buffet night and spent our entire dinner being entertained by the woman who was raising Cain with the staff because they wouldn’t stock the buffet with the particular kind of pizza she wanted. She really put on a show, going to the counter to yell at them and then stomping back to her table to complain loudly to her husband, who was eating quietly, his head sinking lower and lower the more this lady ranted. The staff finally made an entire pizza to her exact specifications and brought it out to her table with a flourish.
There was the time that an obviously novice waiter came by to refill my water glass. He picked up my glass, filled it to the brim from his pitcher, and then seeing it was too full, tipped a little bit of it back into his water pitcher. He smiled and walked away while I was still trying to form words of protest.