In English:
Student: What does the green light [in the Great Gatsby] symbolize?
Other Student: The Green Lantern!

Teacher: There's a fine line between romantic and stalking.

In Physics:
Teacher: What's he first purpose of a pulley?
Student: To pull!

Teacher: I don't know 200. I can barely count to ten. [talking about Phillipinino numbers]

In History:
Student: Aren't there a lot of kidnappings in Columbia?
Teacher: Yeah, Columbia and Mexico, but those are wealthy people for ransom, but that doesn't happen much, I mean, how many wealthy people are there?

Somewhere, I can't remember where I overheard this one:
Student: I never stuck my finger up anyone else's ear.