One's Own Convenience, One's Own Way, One's Way
Noun and な adjective
かって
ほんと、勝手だよね！
You are so selfish!
勝手なことばっかり言わないでよ！
Don't say whatever you want.
「サーモン！フグは五回も浮気したんだよ。そんな男のこと、信じちゃダメだってば。」「分かってるんだけど、でも、彼、私がいないと生きていけないって言うの。」「じゃあ、もう、勝手にすれば！」
"Salmon! Fugu cheated on you five times. Never trust a guy like that." "I know… but he says he can’t live without me." "Well, suit yourself then!"
The hand (or person, as you know 手 often refers to a person) that wins gets to do as one pleases.
The reading for this is weird. It's all kun'yomi, which luckily you've seen before, but still strange. I guess when you do as one pleases you can read kanji however you want, in this case the kun'yomi readings. Do note that there's a small っ in there before, presumably to connect the two readings of the two kanji together.