A robot that is either; a)hideous in nature or appearance; or b)not working properly. Malfunctioning.
That ugly silver thing you got to vacuum the floor, is a total grimbot.
An example would be the robot from Lost In Space.
A friendly but unfortunately hideous looking creature.
N.B. NOT to be mistaken with the Majnemer
Also know as Grimbibbles.
Look at that Grimbot! He camouflages so well in that pile of dung!