"you frosty?" Uses the same meaning as the statement "stay frosty", meaning stay cool or calm. So "you frosty?" Is asking if the other individual is cool, calm, or in a good state of mind.
Person 1: How are you? You frosty?
Person 2: Yeeah, I'm great.
A "jack frosty" is a unique dildo. The dildo is made by the male urinating in a condom, preferably a magnum condom, then the condom is placed in the freezer until the urine freezes. The female then uses the frozen urine filled condom as a dildo.
Caleb: Yo man, how was that girl you took home last night?
Aidan: Yeah, it was great, but she wanted me to do a jack frosty.
Caleb: Oh, thats fucked up.