A while ago I was watching "Skins", the British-made somewhat-comic soap opera about teenagers, on BBC America. The opening scene went something like this:

GIRL: Can I tell you a joke?
BOY: Sure.
GIRL: What do you call nacho cheese? ... Wait a minute. That's not right. (She gets out her cell phone [mobile] and calls a friend.)
GIRL (speaking into the phone): How does that joke go again? ... Yeah, right. ... Cheers. (Hangs up.)
GIRL (to boy): What do you call cheese that doesn't belong to you?
BOY: Nacho cheese?
GIRL: Oh, you've heard it before!

The girl was not a blonde (as if that matters). I found it hilarious, because something similar has happened to me innumerable times. While we're out with friends, my wife will start telling a joke, then get confused, then turn to me for help, or ask me to finish telling it, after she has already spoiled it by giving away the punch line! I hate when that happens! My wife is not a blonde, either, but she might as well be, when it comes to telling jokes!