English slang which can mean feeling poorly or can describe something as useless or unfit for purpose. So if someone says they feel like shit warmed it means they are feeling extremely unwell or under the weather. But if it is their opinion of a device, person or product, it means that the device, person or product is a total WOFS.
Fingering or giving a hand job to someone by putting your hand down the back of their pants while they are sitting, far enough to where the hand extends to or beyond the crotch on the other side.
While sitting in the stands at the Billsgame, I gave my girl a Buffalo Hand Warmer, because we're classy like that.
A work colleague whose only possible contribution to the workplace could be warming their own chair, as they are utterly useless at everything else required of them
A man or woman that a person keeps within a relationship for the sole purpose of not being alone; Company in bed at night and a sexual playmate. The bedwarmer doesn't always know it and is under the impression that the person actually loves him or her.
Ann: Why do you keep him if you hate everything about him?
Jane: I get lonely at night and I don't want to just sleep around with random men
Ann: So he's just like your bed warmer then?