Sick nasty is used to describe a situation, person, or thing so disgusting and gross that it deserves to be called both sick and nasty. Sick nasty can be used in almost all context, I mean what isn't sick nasty?
(orgin the celtic swim '06-07 team)
Wow that shirt is really sick nasty. I just wanted to gouge my eyes out today when I saw Brett because he is so sick nasty. etc
Occurs when playing poker. When either you or your opponent goes all-in (shoves) you show down, and when you are statistically a favorite (usually heavily) to win a hand, the flop, turn, or river (any subsequent cards after the show) give the opponent the unlikely win.
Some donk cracked my AA with his K10 last night, I shoved after the turn and he called. The cards were A,K,J,5. He called and caught his river Q to give me a "sick beat."