How do guys break the touch barrier with a girl?

I see guys who are laying on girls laps, all over them really, and the girl doesn't even think twice about it, but if I were to do something like that I'd get the weirdest reaction. I'm not talking about with breaking it with just girlfriends but with regular friends that you and are girls. Do I have to establish it early on in the relationship?
How do guys break the touch barrier with a girl?
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