Say Ernie

dohohoho

Actually it's Sherbet. People constantly mispronounce it though, so they misspell it, also.

This

now i never even watched the muppets or whatever this is (forgive me) but i'm pretty sure it's meant to mean "sure bert"

I know, but the joke is mispronouncing the word. So, if you used the actual word, this wouldn't be a joke, it'd just be a question and someone responding saying "Sherbet."

Because Sherbet is a soft serve (like ice cream) that was the joke.