People going to the ER for accidents caused while anally pleasuring themselves or someone else with dangerous foreign objects are at least as common as people going to the ER for accidents caused pleasuring themselves non-anally. The worst I heard of was a guy who was whaling away on his girlfriend in the yard and accidentally rolled over on some old rusty tin roofing sheets and sliced his dick pretty badly. Stitches, tetanus shots, and scarring of the cock aren't for the faint at heart.