What is the correct way to crash a class?

If it’s a college class, you can politely enter, take a seat quietly and, if asked, say that you’re auditing. Just don’t disturb anyone.

Is it a big classroom? At least 30 people in there, preferably more like 200–500? If so, just go in and take a seat. Seminar, ask for the professor’s permission. But crashing normally implies you aren’t really waiting around for an invite.

I would always ask the professor’s permission unless it is a large lecture class.

Like this

What did you do?

It all depends on the professor. Usually, they will ask you to stick around or right away let you know if there is room or not. Crashing classes is not as easy as it used to be. Good luck!