1) A combination of gash and crash... turning up at a chick's house with sole intention for having sex.
2) To gatecrash a party with the express intention of partaking in sexual liaisons with females therein.
1) "What happened last night?"
"I gashcrashed at that slapper's flat."
2) Howlarge successfuly gashcrashed a party last week, pretending to be the brother of the birthday boy, and making off with a real stunner.