Yetti, not to be confused with Yeti, the big white thing that eats skiers, means someone who is a computer geek or is looked upon as geeky by others.
It was invented by a group of college kids several years ago so they could make a joke of a kid without him being able to retaliate with some geeky answer
Person 1 "Wow I just got the top score on Time Crisis 3"
Person 2 "You are such a yetti"