The moment in which blood fills up a man's penis about 3/5ths of a way; it is not aggressive but a respectable girth/length. Better than being flaccid, and slightly better than a half chub for all situations. You would want a party chub at almost every occasion, especially at a party or even at a business meeting.
Kaya: Hey Justin, why is your phone right there? points to pocket
Justin: Oh, it is not my phone. It's just a party chub...
Kaya: Oh! My mistake! blushes with excitement