How do you do the peck dance?
The peck dance is when a guy (well, or woman I guess) alternatively clenches one pectoral muscle in the chest and then the other pectoral muscle. IF you don't have enough muscle there, it won't be noticable (or look incredible silly) if you try it.
However, if you're built like Fabio (the guy who does the covers for romance novels) then you can rip your shirt off and make your pectorals bounce, I'm sure some people would think it was cool.
You have to have very strong pectoralis minor and major muscles (chest muscles); you will be able to flex and relax them when they become strong enough, which makes them look like they're “dancing”.