a very ambiguous term based on whether not one is or isn't actually in a fraternity. In the South, among actaul fraternity members, fratty refers to the sterotypical southern frat guy image, that of new balance tennis shoes,ralph lauren polo shirts, rainbow or reef sandals,patagonia jackets, ray-ban/costa del mar/maui jim sunglasses with croakies, private schooling, shaggy hair and khaki shorts...etc. It is used as an adjective to describe things associated with said lifestyle.
Among other people, usually GDI
or those in the north, fratty refers to a differently held stereotype of a frat guy. Such stereotype includes abercrombie t shirts, spiked hair, tribal tattoos, cargo shorts, popped collar...things that southern "fratty" guys actually find ridiculous, especially collar popping.
My professor is totally fratty, he wears polo to class every day and I saw him with croakies the other day.
That guy was looking mighty fratty the other day in a seersucker suit with a bowtie.