Brett makes his only appearance in "Daria Dance Party". He and his brother Brad goes to Cumberland High but attend the Lawndale High dance portrayed in the episode, where they try to woo Daria and Jane. They have some success until they reveal themselves as Upchuck's cousins. Brett was less visibly bothered the girls fled.
(This makes Brad and Brett highly significant: the first and really only time that Daria and a guy show mutual interest with no problems!)
They seem close to their cousin "Chuck", turning up to see his DJ act & hang out with him afterwards - Brett even does the same 'feisty' growl Chuck does. They also knew who Daria meant when she called him "Upchuck" and showed no reaction to it.