what is OMGUS?

[The Fonz]

In my experience, and OMGUS later in the game is more likely to come from an emotional/inexperienced townie. A Scumbag trying to defend himself will know that simply voting for the other guy won't help.

IMO, there's another layer to that. An experienced scum is less likely to be thought to be pure omgussing, yet the person who's your strongest accuser is the townie least likely ever to support you. By attacking that player, you limit the number of pro-towners you alienate, so keep as many potential votes on-side as possible.