Charlotte-Douglas hired their attendants in 2006, so they're celebrating a five-year anniversary. Don't take that as a reason to tip, though. Their purpose at CLT is to regulate bathroom traffic and see to the cleanliness.
Try as you might, you can't escape the attendants; they're in every restroom at CLT. So do you tip? According to other travelers (and this extensive blog post questioning the cleanliness of the CLT ones in particular), the helpers have a tray of goodies. There's mouthwash, tissues and other niceties. It's wise to tip if you use something of these, above and beyond what you'd normally have in an airport restroom.
Our friend chose not to tip because, as he put it, "I don't tip for doing things I could do myself, and faster."
Bathroom attendants anywhere weird us out, but it seems the ones at Charlotte airport are successful in at least one regardwe're talking about them right now, aren't we?