When a guy spreads out his a$$hole with his hands as far as it will will stretch.
Sadly, it's normally one of the first things someone sees on the internet, whether they get emailed it as a joke (It says "Click here for cute bunny pictures" when it's actually goatse) or they just stumble apon it.
It supposidly is a fetish for some. But, you just gotta think "Who the eff likes that?" since it's so gross.
NOTE: If you're reading this because you don't know what goatse is, DON'T google it! You'll be scarred for LIFE!!
Guy1: *Opens email from Guy2*
Guy2: *Laughs to himself, knowing that Guy1 is probably reading his email*
Guy1: *Clicks on link from Guy2's email that says "Click 4 pix of hot chick*
Guy1: *Sees pix of Goatse* EAAAAAAAHHHHH!!!!!!! *Gags*