Lyric discussion by Pomaceous 

Cover art for Be Gentle With Me lyrics by Boy Least Likely To, The

This song sounds happy, but it's actually rather bittersweet.

I believe that it's about that feeling that you get when you're excited about being with someone--in love--but you're also scared of comitting yourself for whatever reason.

The "because I'm mental" might be a clue as to the narrator's temperment: he might be warning his significant other that he can get crazy, that he has many problems, so she'd better be careful with him.

It sure sounds happy though.