The meaning of the sentence doesn't change if you say "growing up", "acting like an adult", or "taking responsibility for yourself".
I should also note that I'm not exactly a fan of your willingness to screw someone you don't respect. But your lack of desire for a real relationship isn't my problem.
I'm not sure why you feel I don't respect someone simply because I don't want to work with them.
Had I thought of them, I would not have used any of the phrasing you suggest because they are insufficiently derogatory.
Consider this guy: The rejection of the other employee [by Julie Ann Horvath] led to...an internal battle at GitHub...hurt from my rejection, started passive-aggressively ripping out my code from projects we had worked on together...
"Act like an adult" doesn't have the same ring as "grow a pair" (although in this case, "stop being a whiny bitch" would be my preferred phrasing).
I should also note that I'm not exactly a fan of your willingness to screw someone you don't respect. But your lack of desire for a real relationship isn't my problem.