Felix is defending himself and Oscar in court after they've been arrested and charged with scalping tickets. Calling to the stand the woman to whom he'd offered an extra ticket (for free), he gets her to concede that he'd refused the $15 she'd offered for it before she claims he'd "held out for more". Felix tells her to think carefully, and asks if he'd really asked her for more money. "Not exactly", she admits, "I just assumed...", and Felix pounces on this:
Felix: Your Honor, may defense counsel use that blackboard?
Felix: Thank you, Your Honor! Miss Olem, you should never "assume", because when you "ASSUME" (writing the word on the blackboard), you make (circling) an "ASS" of "U" and "ME"!