Someone who isn't very attractive, but isn't horrible.

A male/female who isn't attractive earlier on in the evening. However, when 2 am comes along and the bar/club starts to close, you are willing to take him/her home.

2AM can be used anytime of the day.

Two a.m.' He swallowed, then said, "You know. The person you can call at two a.m. and, no matter what, you can count on them. Even if they're asleep or it's cold or you need to be bailed out of jail...they'll come for you. It's like, the highest level of friendship.