Avoid a social faux-pas on your lap

That's from XKCD, which has been my favourite webcomic for awhile now, it's brilliant. According to the header it's; "A webcomic of romance, sarcasm, math[s], and language." which pretty much perfectly sums it up - although there's quite a few science-based jokes in there too.

If you've got some time to spare, I'd recommend reading your way through the entire archive - and don't forget that each comic has its own mouseover too, which is sometimes even funnier than the comic itself. Some of the comics are beautiful, some are wonderfully satirical observations on life, others are obscure (yet hilarious, if you get them) mathematical or physical jokes) and yet others, like above, are just good old-fashioned geekery.