Dumb and Dumberer - New Dollar Bills Made in 1986?
In the scene where the class goes on a field trip, watch closely when the teacher goes up to the guide and goes to hand her a tip. The lady says "Sorry, we don't accept tips." Than the teacher says "Give to the tour twice, and speak slowly." When she goes to hand the 5 dollar bill to the guide, you can notice that it was one of the new dollar biils made in the 2000s, not one of the older dollar bills which she should have been holding.