How to troll people:

Person 1: What did the cactus say to the other mean cactus?
Person 2: 'You're a prick?'
Person 1: No silly, the cactus said nothing because cacti can't talk!

Later:

Person 1: Hey what did the cactus say to the other mean cactus?
Person 2: I thought you already asked me that-
Person 1: But what did it say?
Person 2: Well it didn't say anything because cacti can't talk.
Person 1: No you intellectual it said, "You're a prick."