First time I've ever written one of my comedy ideas down and shown others, but please don't lay back on your criticism! Not so much a sketch as a 10-second snippet that could be inserted into a longer film or scene.
[Scene: A man sits in a cafe in South London. A television is showing a news programme. Behind the man is a large window out of which a mostly-quiet road is seen.]
Newsreader: Police have issued an alert regarding a series of assaults that have occurred in South London today. The events are believed to be related as several people have reportedly been blinded in random attacks.
[As the newsreader speaks, a man with no trousers steps into view in the window. He unfurls a set of Venetian blinds then runs across the road, swiping the blinds at an unsuspecting passer-by's back and backside. The passer-by collapses to the ground. The assailant takes a quick glance in either direction, then runs off.]