Mushroom.

[William51]

Why was the mushroom always happy ?. Because he was a fungi.

[roopower]

Hmmmmm, sorry but I fell out of my cot laughing at that one!

[royfromaus]

That old chestnut.

[bobbinwales]

a christmas cracker favorite- - even though its pronounced fung ee not fun guy, . Yours sincerely SCrooge

[Chipchopper]

I first heard that one in portabello road.
not mushroom for any more, there Will ;-)

[zabado]

Christmas cracker 1978.