Skateboarding is ‘mainstream’ by all definitions, and there’s a noticeable gap in the counter-culture sports world.
I guess you could consider electric longboarding or scootering in some cities as going against the law, but nothing screams teenage rebellious angst to me like urban skim boarding.
Just grab your skim board, find your city’s various fountains and get to skimming.
The local authorities will definitely try to kick you out, you’ll probably get injured, you can listen to some sweet music that nobody has heard about, and you can wear some wacky clothing to really express yourself.
It checks all the boxes to fulfill the counter-culture’s never-ending need to ‘rebel against the man’ and make their mom’s worry about them.