I don't believe there is a TM issue with this because its a broad term and not an exact term otherwise there would be alot of companies battling each other over the term frosty, like "Mr Frosty" , "Frosty Treats" "Frosty The Snowman" etc
Personally, I don't think there would be a TM issue with a generic term like frosty & especially with a popular term like "have a frosty one". I would say this name is worth at least in the Low $xxx range if not a lot more if you find a beer company.