VERB
The act of attending a university lecture for a class you do not take.
Derivative of gate crash
Reasons behind this behaviour vary... One could lecture crash to keep a friend company, to hide the fact that they have no one to hang out with during a break, to try before you buy, or maybe just because they find the subject interesting.
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.