His hair must smell like shit

You just got fucking dumped bro

What I'm getting from this is that Nick has been making some unwanted advances upon Gio aside from merely having his hair cut. Gio has respected Nick's orientation but is not personally interested in going down that particular "muddy road". Nick has not respected Gio's position on the subject and is pushing the boundaries to a point that Gio is no longer willing to tolerate.