A derivative of "idiot" or "pratt", Helmet fuses the semantics of the end of a man's penis and the un-cool nature of the common bicycle helmet. It is most commonly used in a jovial manner when laughing at a friend or aqcuaintance with another friend.
It can also be used to describe a person who is not a friend, who has committed an action upon those in the circle of friends which had malicious or vengeful intent, but ended up being a source of laughter to those inside of the circle of friends.
" You heard that Shaun is away this weekend seeing that minger from Blackpool ?! "
" Haha is he?! What a Helmet! "
" Did you see that lad come to push me away from that girl he was trying to pull and then slipped on the dancefloor?! "
" Yeh! What a Helmet! "