I bought my friend an elephant for his birthday.

This classic birthday gag gets its power from a perfect collision of absurdity and wordplay. The setup presents us with a ridiculously oversized gift, creating a situation that is impossible to ignore. The punchline then cleverly plays on the dual meaning of the phrase "Don't mention it." Is it a polite, standard response to a "thank you," or a literal, desperate plea to ignore the giant, hay-munching mammal now standing in the living room? The humor lies in that delightful ambiguity.

The joke is, of course, a brilliant literal take on the classic idiom "the elephant in the room," which describes an obvious truth that is being studiously ignored. While giving a pachyderm for a birthday is unheard of today, elephants were occasionally given as diplomatic gifts between monarchs in history, making them the ultimate status symbol. The joke perfectly combines this high-status, impossible-to-hide gift with a common phrase, creating a wonderfully silly scenario that's hard to forget.