While it is not as bad as the other examples here, I once got accused of throwing a can of cola on the ground. There is a bit of a story behind this:
I was around 11 years old and walking around with my nephew and younger brother. It was carnaval, and because it was rather warm, we all got some cans of cola. We were walking around, on a schoolyard (It was nearby and you had room to play).
There were two other groups of children. One were older, trying to impress each other with how "cool" they were. The others were a bit younger. Eventually, the older ones got bored, threw away the cans they had and left. I didn't really notice, didn't know the guys.
Suddenly, I hear someone, in a really obnoxious voice "Aren't you going to pick that up?".
It was one of the younger kids. I replied that it wasn't mine, that the other group threw it.
The kid then said "Yeah right, then why is there a bee on your costume?" I looked down, saw the bee and flipped out, afraid to be stung.
The younger kids then walked away laughing, thinking that justice had been served (cartoons made you believe that stuff =P)
To this day I can't get over how unfair that was :<
Sheesh, what a rant.