1.
Coming down from any sort of "high," whether from drugs,
adrenaline, excitement, etc. In other words, it's when the good feelings go away and you get tired.
2. Interrupting or attending any
social gathering you were not specifically invited to.
1. I
crashed pretty hard, got really tired. and went straight
to bed.
2. He's a prick -- always inviting himself to stuff and
crashing parties.