Try this:

Imagine Ernie saying to Bert, "Hey, Bert! Kiss my ass!"

Now try to imagine Bert saying the same thing to Ernie. You can't do it! Bert could never tell Ernie to kiss his ass! Bert could think, "Ernie! Kiss my ass!", but he could never say it. He's far too hung up. Bert's a pressure cooker waiting to explode. Don't be surprised if someday you see a newspaper headline that says:

Famed Muppet 'Bert' Guns Down Dozens in Cookie Store Shootout!