The Giant Rat was a level 5 semi-boss silverfish mob that spawned in the nest at Farmer Cevalus' Farm that used to drop The Wedding Ring. Due to it having been nigh unkillable at level 2, the Giant Rat has spawned many jokes about it, usually made by Pre-Gavel players. The quest involving the mob was replaced in the 1.17 update, and thus, sadly, the Giant Rat was removed. This resulted in even more jokes in the community regarding the importance of re-adding the giant rat into the game.
In the 1.18 update, the Giant Rat was added back as a normal mob.