Fluke tends to be a positive appreciation of good luck, rather than a denial of the win. It can be used to playfully reject someone's win though, or to be humble about one's own win.
(In bemused disbelief that someone won a football game): "Jeez, how did you score that goal? You weren't even kicking it right. What a fluke!"
(In happy humility after winning): "Thanks. It was just a fluke really".
(When someone beats you in a game, but you're convinced you'll win next time): "Fluke! Let's go again."
(To tell a story without it seeming boastful): "Well, the whole thing was a fluke really. Back in early Spring, I..."
at 7:26 tiffany calls jennifer, "hey where the hell are you at? it's 7:26pm, you said 6:30pm"
jennifer, "oh yea, i dont think im going any more."
tiffany, "damn, you FLUKED me.....well gee thanks for letting me know you changed your mnid foo! uugh you damn fluke!"
Meaning "Slut" . A trashy female that sleeps around. May also be considered a prostitute. Uses birth control but doesnt want to have to pay for it. (also see definition for cheap)
Being the fluke you are I know you will do me right.