A sketchead is British slang for a douche-bag. And the stereotypical douchebag thing to do is to turn up to parties uninvited.

Also a song by Arctic Monkeys, from the album "Cornerstone"
"David is such a sketchead, doesn't he realize we never invite him to anything for a reason?"

Leave a nice comment or I'll buy your Nan flowers

Jokes I ain't that horrible.

Or am I?

You just checked this spoiler hoping for a continuation of the whole spoiler thing. Get baited.