Imperial Guard.
Their strategy seems to be "Stand here in a big pile, then become bloody when the giant army of orcs/chaos/stay puft marshmallow men crushes you. Oh, and anyone who wants to leave? I'll shoot you."
The Guardsmen are (in the novels, anyway) portrayed as being pretty much the weakest beings in the universe (or outside of it) who still insist on fighting. They're the onstage warm-up act for the Space Marines. Even the all-female army (forget what they're called) is much, much stronger than them.
At least Grunts are pretty tough. I mean, they can kill Marines on their own. They can kill pretty much anything that isn't a Spartan on their own.