Yup, i have encounter something like this some time back.
I was on the train with my friend after school and these groups of
young adults, about 7, boarded. All age 18 to 20 like that. Started
talking damn loud and 90% of their conversation are foul words,
making it pratically meaningless.
Then one of them flicked my friend's ear and pretend he didn't do
it. obviously picking fight. Next they pretend the train shaking
and cannot stand properly, so lost balance and pushed us.
Felt like punching them, but me and my friend were outnumbered.
Also, we were in uniforms, and my school is one of those the public
always like to write to newspapers if they saw the students
misbehave.