I recall seeing him with Little Richard, who kept referring to him (to Rickles' seeming frustration) as "Don Wrinkles". I wondered if that was something that they cooked up beforehand, as it wasn't Rickles' usual modus operandi to let people get the best of him.
It amazed me that people laughed along with his ridicule of them. I think the worst was when he hosted the Tonight Show, was doing interviews in the audience, and said to a woman with protruding teeth - "Are you Japanese or do you just have a lousy dentist?" And she laughed.