In the scene where Dallas (Matthew McConaughey) finally strips, there is a point where he rolls away from all of the women holding his crotch. This is because the extras got a little bit too excited and accidentally ripped his g-string. Instead of stopping the dance, he just incorporated it in.
The character of Tarzan, portrayed by Kevin Nash, wears a knee brace during his routine and goes with the idea that stripping is all his character knows and is doing it past his prime. This wasn't in the script but came about when Nash showed up on set with the brace on and explained that he wouldn't be able to do the routine properly unless he wore it. Kevin Nash is a professional wrestler with a history of knee problems.