It possible that someone can hurt a competitors rankings with adult links. But remember that it's possible to win the lottery.
Originally Posted by whatthehell
Matt Cutts has discussed the topic and he says that Google trys hard not to allow a competitor fo hurt your rankings with spam links.
The short answer is we try really hard to make sure that one person can't Google bowl another person. You try to include it in your algorithm so much that you don't want those links to count, but you don't necessarily want anyone to be in a position where somebody else could try to hurt you....
We try to make it so that it doesn't cause a drop in your rankings (if a competitor tries to hurt you). We try to do stuff algorithmically, we use manual means...we've been pretty clear that we do not like paid links and we take action on it, but at the same time, we try very hard to make it so that just because somebody else doesn't like you, they can't submarine your rankings and things like that.
How Google Handles Google Bowling | WebProNews