Anthony wants to prance badly but he's singing with his arms crossed to keep his feminine gestures to a minimum
Interesting observation. He's conspicuously not wearing a second shirt here, so my guess is that his ten year old NYPD T shirt is a little snug on him and his usual gay gyrations might accidentally expose his flab, so he's making a conscious effort to cross his arms and do everything he can to not jiggle or have his shirt ride up. His second shirt acts like a combination security blanket/cape, disguising his cave amphibian-like body while he lets his fag flag fly.
Also there is a woman near him, which always makes Nana uncomfortable and nervous. His body language always visibly changes when he's in proximity to any woman, as he's secretly repulsed by them.