Ever since I've been on a crowded subway, I've always had the thought of groping a girl, whether it be my girl or a stranger standing next to me.

I'd probably "accidentally' brush a hand or something against her butt and she how she reacts, or maybe even slightly grab it a bit. And if that goes well then perhaps keep my hand there and give it a good feel.

By chance she enjoys it or doesn't seem to fight back, I may as well face her back and take a feel at her breasts. Then I'd move my hands downward slowly and give her a nice finger fuck while massaging her breasts until she orgasms or the ride ends.

Hard to find a good picture with real people, so an anime style one instead.