As CommanderPaladin said, your armatar is not a rat. Here's the rat armatar for reference:
Anyway, here are some weird armatars I have seen:
Depressed King:
Spider (seasonal):
Ghost (not seasonal):
Ghost (seasonal):
Two of the armatars are seasonal, but I have seen one or more users with them. This is a short list, but I don't have a single answer, so I will explain the weirdness of all 4 armatars (btw, the rat armatar is not weird):
Depressed King: I once saw a user named exicoasterpath with this armatar. Anyway, it's the depressed part that makes this armatar weird.
Spider: This armatar is seasonal, but I saw ninjachampion with it. Also, spiders are weird, so this armatar is weird.
Ghosts: Two of the armatars are ghosts, but one is seasonal. However, I have seen HowManyGhosts with the seasonal ghost. Also, the head of the non-seasonal ghost looks a lot like the Depressed King armatar. Since that armatar is weird, the non-seasonal ghost must also be weird. The seasonal ghost looks weird because of the boo above it.