Grinding up against me on a crowded train giving me an erection?

A few times on a crowded train, I'll have a girl in front of me. I'm pretty talk, 6'2". As it gets more and more crowded I am pushed up against her and start getting an erection. I pull away a bit to not have her notice, but she'll fall back on me and continue to grind a bit. This continues the whole ride for 20 minutes.

She's doing this intentionally right?
Grinding up against me on a crowded train giving me an erection?
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