Source: Public Service TV spot from Guinness featuring the animated Brewmasters.
1) Acronym for the message of above-referenced spot: Use Common Sense And Always Know When You've Had Your Fill
2) General sign-off to your buds as they head out for the pub/club/party
3) Expression of disbelief, akin to WTF
1) Pretty self-explanatory
2) Guy 1: "I'm heading out for the club to get laid, drunk or both.
Guy 2: "Good luck, Dawg. UCSAAKWYHYF."
3) Guy 1: "Dude... when I was out, I chatted up that 'girl' you were drunk-dancing with last week. 'She' asked for your number - and said thinking about your pants gave 'her' a boner!"
Guy 2: "UCSAACWHYHF!"
A loose woman who gives it up for brewmasters or owners of breweries. This type of woman can be found in other places such as concerts, comedy clubs, anywhere where there is a well known individual who has gained enormous amounts of success. She uses her female genitalia to gain fame from famous brewers and brew owners.
Look at that brewpie, she'd spread for anyone with a bag of hops.