It got its name from the song Mr. Bojangles:
"I knew a man Bojangles and he danced for you ..."
Check out the Bojangles on that guy!
One could also just start singing the song to alert their friends without necessarily pointing out or bringing attention to the fact you're checking out someone's package.
its acutally just a word that you use to portray an emotion. it can mean pretty much anything, it all depends on the tone of voice you use with it. it is also commonly used to describe tarantulas.