I'll add another vote...I've commented about the length of songs before, totally not meaning it as an insult.
For me, it's usually a salsa or merengue, and it just keeps going...and going...and going... I'm a smoker, and after a while, I feel it. Which is all I've ever meant.
I don't think I've ever had anything mean said, but the rudest thing every done while dancing was the last dance of the night one time. It was supposedly AT (but I'm not buying it), probably AmTango or something, and the guy absolutely COULD. NOT. LEAD. He never said anything to me, at all--not before during or after the dance--but he did resort to actually kicking my foot to try and make me step where he wanted me to. Repeatedly. I mean, I'm a beginner and I miss leads plenty, but I can follow decently at least. Or so I've been told. But to actually KICK me?!?!
I was so shocked I had no idea of what to even say at that point. Hmmm...I guess a comment about the length of the song would have been VERY appropriate!