Welcome to the club buddy! I've passed on threesomes due to alcohol, kicked my bestfriends ass, sarged my girlfriends friends, oh.. That list is long..!
"Should one generally avoid negging, or being too "up there" when being approached? Even if the girl approaching you is of high value?"
Well, it's very situational, if she's nice to you, and approaching you, then she's most likely already interested, and there's no need to neg her as far as i can see
The general rule for me is atleast only neg HB8-9-10's and don't overdo it, max 3 negs should be enough. But you have to review the situation and find out what's best.
And for the alcohol thing.. Unless you scarred her deeply emotionaly (which u most likely didn't) I'd just tell her that you're sorry, have a laugh about it, and move on about it.. Shouldnt be a bigdeal.
Good luck!!