What does it mean if you "poke" someone on Facebook

[BrokenBananaTantrum]

Is it just a "hey how are you?" thing or is it a bit rude?

Polite I think - just a nudge to say hello

Indeed, polite action, but perhaps made to sound rude to 'market' Facebook, IYSWIM.

I avoid Facebook as much as I avoid Twitter

Loved the pre-election blunder made by David Cameron about Twitter. Wish I had said it first !

Thanks. Not on Twitter. Don't really understand how it works What did Dave say?

its not really done anymore. just a sort of hey, how are you. i remember you exist sort of thing

Well, his meaning was "Twitter is for Twits" but actually said 'Twats' and only afterwards did some advisor mention that 'twats' has a more offensive meaning in many parts of the UK.