I agree that nice can be ambiguous but when I think of what it means to be not considered "nice" I think "untrustworthy" and "sketchy".
I'm going to go out on a limb and say that I know a lot of your friends and while I wouldn't say that "nice" is the first word that comes to mind when describing them I would say that "fun" is, and "untrustworthy" and "sketchy" are not... mostly.
"Nice" and "fun" are not mutually exclusive.
I like fun people as friends. I like people who are nice and fun.