I have to agree as a male the flirting looks very awkward from a straight male perspective. More to the point if I flirted like that with a women at a "venue", she would probably lose interest pretty fast or assume I'm probably not really into women. You can call this whatever you want but we react unconsciously from body language that dictates our responses plus they certainly could have chosen a more "neutral" flirting animation.
However with all that said I just chalked it up to Sims 4 weirdness, I mean the woohoo acceptance animation involves a fist pump into the air.
When was the last time you pumped your fist into the air when a partner agreed to uh...woohoo in real life? I suspect you might get a laugh the first time but after that well...I don't the reaction will be the same lol. I mean we have a "bro" trait in this game that I suspect never gets used but they invested time in creating it...