What if a girl touches me down there?

what do I do if a girl puts her hand on my pennis?

You like it... lol.
No, if you are uncomfortable, tell her.
If you like it, let her I guess. :- )

You slap her across the face and say, HEY!!! That's mine, get your own.

J/k... well I'd hope you'd like it and just go with it. If she took the initiative to go for it then one can assume she knows what to do or, if not, then she knows what she wants. And if she just rests it on your pants or whatever then, again, you can assume what she wants. So you take it out and you take her hand and rest it on it (And I would hope things would go from them). Good Luck? (I dunno if you were asking just in general or it's happened to you, lol)

IN THE FIRST PLACE DID SHE EVEN WAS ABLE TO REACH DOWN THERE???