When I was in 8th grade, around 13 years old, there was a kid who I was sort of friends with (we'd talk and play together with other kids once in a while, but weren't real chummy). I commented that both our houses were the same distance from the bus stop (they really were), he said that his was closer, I disagreed, so he knocked me down and put me in a choke hold.
I think that's the dumbest I can think of.
When I was a senior in high school, I got jumped by 5-6 jocks because I accidentally cut one of them off in traffic on the way to school in the morning.
I had a couple years of MA training by that time, so I managed to get out of it with only a minor injury (abrasion on my back from taking ukemi (breakfall roll) on pavement

)
Fast-forward to college, I found myself in the middle of one of those strange bar fight phenomena where people uninvolved in the original conflict just start fighting with strangers. I always thought it funny when I would watch those western movies where one guy in the saloon is caught cheating at cards and all of a sudden the whole place is filled with people fighting eachother. This was just that sort of thing. I just happened to be in the vicinity. A fight broke out; some guy I was near that wasn't involved in the fight either got pushed or bumped or something - collided with me as I was trying to grab my drink off the bar and get some distance away - then turned around and started throwing punches at me. By this time, I've had several years of training, and the thought of someone trying to fight me was quite ammusing, so with a smile on my face, I angled myself away slightly, put my hand in his face and allowed him three or four more tries to hit me. He eventually got a discouraged look on his face, gave up and turned back around to see what was going on with the initial conflict. I finally made it over to my drink, grabbed it and walked away laughing.
There's been a few other stupid situations (mostly involving drunk frat boys - they're the most fun to play with

- which are in numerous supply here in a college town), but they all de-escalate quite rapidly when they realize that I'm not going to play by their rules. I actually submitted one big dude who tried to wrestle me down by slipping out of his holds, popping him a couple times lightly in the nose, then dropped down to execute my - now famous - big toe lock (he was wearing sandals). He gave up right away.
All-in-all, I agree, all fights are stupid, but the ones with untrained fighters are the most fun!