was the "thing" black? if so, your turtle just showed you his jewels! if it was pink, however, could be his intestines (which points to other concerns). the penis-showing part is normal. UNLESS he forgets to put it back inside, then theres nothing to worry about.
if he is fanning and fluttering at your female turtle, he may be sexual mature to reproduce. although this could be part of his mating ritual, it could also be a sign of aggressiveness. also, there is a member on this forum that had one of her turtles bite the turtle's penis while he was fanning. ouch :X
http://www.redearslider.com/forum/viewt ... highlight=
are you sure that the other turtle is a female? if so, are you prepared for eggs? you may want to consider separating them because males are known to harass females.