Apparently most people here don't get the obvious reason driving Chad...

Chad's goal was not to hurt either "some girl ripe for the taking"(she happened to be Christine), or Howard. Sure he enjoyed hurting them, but that was a bonus, not the main goal.

The whole "let's hurt somebody" plot was engineered specifically to sabotage Howard without him realizing it (too distracted by Christine) and thus Chad getting hi job without Chad's fingerprints being anywhere (which is why he stops short of telling Howard why he did it, he just states "because I could" vaguely enough so that Howard doesn't realize HE was the target, not Christine, that way he wrongly takes away that Chad went out to hurt this poor girl just for fun).

It really is that simple. Extreme, but similar stuff happens all the times at work when competitive coworkers trip each other up to score that promotion/assignment/etc.

Don't get me wrong. I don't deny Chad clearly has issues (sociopathic, woman-hater, etc) which is why he chose that particular way (through hurting an unknown woman) to get the position he wanted and not a different one (there are many ways to accomplish the same goal, say sleeping his way to the top or work harder?).

However, in real life such a callous character would ruin his reputation quickly and nobody would ever trust him with a mop (what manager would ever have him in their team knowing what he did). Really short-sighted (unless Howard never really puts 2 and 2 together, or anyone else).