With your Hypno friend whose dressed as a schoolgirl because she wants to live out her, 'molested by a stranger on public transit' fetish. So you push her up against the window, get behind her, and just put your fingers in there. The more crowded the train, the better. Also works really, well with your drowzee dickgirl friend, but is slightly less discrete. SUPER less discrete when she blasts the train door with her goo. Might want to try that one at night.