In the beginning of this myth, Loki disguises himself as a bird, and that disguise is a little preview of what's coming later on. Geirrod pretends to be host of the year when he's actually got plans to murder his houseguest. In both cases—Loki as bird, Geirrod as gracious host—what's inside doesn't match what's on the surface. And in Germanic warrior culture, there are few things more uncool than that.
On the other hand, though, there's Grid. She proves that her good hostess act is the real deal by giving Thor all the dirt on Geirrod. Plus, she lends him some objects to help him defeat the baddie. She's kind of like the yin to Geirrod's yang, the straightforward good hostess where what you see is what you get.