Mr. Belding: Go to class, learn something.
Lisa: Yeah, 'I have all these problems and there's no-one ever there for me. I talk and talk and talk but no-one ever listens.'.
Zack: You know, I've finally found out the best thing about high school, once you graduate you don't have to come back.
Answer: Zack is always good for a sarcastic jibe. Lisa was written as the most fashion and make-up conscious of the Bayside High girls. She was also portrayed as serious and somewhat prissy. The "crack your makeup" comment was a throwaway line. Zack was suggesting Lisa doesn't often get overly excited for fear of having to reapply her face. The line is met by laughter and screeches from largely adolescent female audience that seem out of proportion to the humor. "Saved By the Bell" audiences were rather prone to such excessive ebullience for no apparent reason. The reaction didn't last long, and the scene moved on quickly.
Michael Albert
Yeah that doesn't make any sense.