Not surprising, window cleaning isn't likely to attract the brightest bulbs. They might be able to type, but it doesn't automatically mean they've got manners.
We all like a bit of banter, sometimes its a fine line between stupidity and highly humorous. Just ask Spike Milligan. You don't need to look to far.
They normally think very highly of themselves, have a superior opinion of themselves and their understanding of just about everything meaningless, like to be the centre of attention, make out they're bloody hilarious, have an opinion on everything (generally formed from browsing wikipedia) they always know someone who's also done whatever is the topic of conversation but generally bigger, faster or funnier.