An individual who is currently annoying the peace of an "in" group.
Somebody who's usually cool, randomly does or says something really lame and annoys the fellow cool people.
Some random white guy walking into a circle of mexicans and says "hey homies"
you're chillen with your fellow coolmo's and suddenly a best friend stupidly says "so, who saw Scrubs last night?"... he is currently labled an Impest.