The act of popping up the collar of a polo shirt, so it covers the neck.
Twenty years ago kids in ghetto wore their collars popped, now it is a trend among frat boys and preps.
A common look for the frat boy is to wear a pink polo shirt with the collar popped. The pink shirt fools sorostitutes into thinking that frat boy is comfortable with his sexuality, when in reality, every sixth word out of his mouth is faggot.
And here we see a fine specimen of prep. Note the sandles with socks, meticulously groomed hair, and popped collar.