The act of pressing ones hand on a supposid girls crotch to check for a penis. This act is to help discover if a "woman" is truely a tranny or not.
The term press check was lifted from the firearm community when dealing with firearms. In this form, the act is to check to see if the firearm has a round in the chamber. Similar to the the other definition -- Checking to see if the "girl" is loaded.
"What!?! You got blown by a tranny in Thailand? You didn't do a press check before you dropped trow? I call bullshit, faggot!"