did you hear about the guy who got fired from the keyboard factory? he made a rookie mistake - he left out one particular key:
f u
n
n
y
oh man, did you get that one? it's a pun, because he left out the f key and i had to put it in for him. get it?
ha ha ha, oh i'm hilarious, am i right?
so, in the joke, the guy was working at the keyboard factory, right? and he got fired because he made a big mistake - he left out one key from the keyboard, the letter "f". so the f key wasn't there, so what did he make? a "rookie" mistake, but i fixed it by adding the missing "f", which made it "funny" instead of "rookie" - a pun! the joke is that it's a play on words, because he made a "rookie" mistake.