Hitch Ball
I did lube mine when I used to tow a trailer, but I also kept the ball covered when not in use and cleaned it frequently. Lubrication is good, but dirt and sand in the lubricant is worse than no lubrication at all. And these guys are right! A greased ball does seem to just jump out and wipe the black stuff on anyone who gets near it! A seldome used ball, or one not cleaned frequently, is better left dry.