Context: Kotobuki Ran 寿蘭 tells Hoshino Aya 星野綾 to stop with compensated dating.
oyaji matten'no? yametoki na, enkou nante sa オヤジ待ってんの？やめときな援交なんてさ [You] are waiting for the old man? [It's better if you] stop, [with stuff like] compensated dating.
matten'no is a contraction of matte-iru no 待っているの.
yametoki is a contraction of yamete-oki やめておき, a ren'youkei 連用形 such as this before the na な particle forms an imperative sentence, i.e. she's commanding the other girl to stop.
