Or so they say. I've asked my male friends who utter this mantra what it means.
They say that they take women out on dates, talk to them, hold doors open for them, and such -- are in fact the very definition of a "nice guy". And yet, all they end up with is friends, rather than girlfriends who will make them feel special (and, hopefully, get them laid) -- that is, they "finish last".
So, let's analyze this. These "nice guys" expect that the ultimate chivalrous act of being friends with various women is not an end in itself, but rather will lead to them acquiring a girlfriend. They're frustrated because all this work they've been putting in actually talking and listening to their female friends hasn't paid off.
Not very nice, is it?