I haven't heard the Zac Brown song, but 'ass' always seems like a comedy word to me; as far as I'm concerened it's interchangeable with 'butt'. Which makes it even funnier when it is dubbed out. In Nickelback's Rockstar they even dubbed out "Gonna dress my ass in the latest fashion' on some stations over here - crazy!

I'm not a fan of profanities in songs, but sometimes it can be very effective. The aforementioned 'You Oughta Know' is a case in point, the angst just wouldn't work without that turn of phrase.