Don’t do it. Friend had 2 chances; you were a sap to even offer in the beginning.
Here’s your way out: “Sorry, something’s come up…”
BTW, why do I sense that you *will *do it? If you do, be sure and clean the toilet and the shower extra clean-I hear that she can’t stand a dirty bathroom!
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First of all, he didn’t expect you to do anything, you volunteered, right? That’s going on what you told us.
I think the girlfriend is a douche. But the guy is still your friend so if I were in your position I’d still help him out. That being said, if he’s letting her get away with this shit… I guess I don’t know what I’d do. Maybe move all his shit and leave hers in boxes outside to move in when she gets back or something. 
crazytooth615, if he’s a good enough friend for you to volunteer you and yours for the god-awful task of moving, how is it that he’s not a good enough friend to just be honest? Is it not possible to simply say, “I find it curious that your girlfriend expects everyone else to move her. What’s the deal? My offer still stands, but without her actually being there on the day, I feel more like her unpaid slave than your good friend wanting to offer a helping hand.”
Who knows - there may be a reasonable explanation for her outrageous behaviour. At worst, you’ll alleviate the feeling that your good intention is being abused. You will probably deny yourself years of The Day That Lazy Bitch Suckered Us In To Moving Her And Other Stories, though.
The friend didn’t volunteer the OP. She said she volunteered herself (and her boyfriend).
I think it’s reasonable only on one condition: all her shit is already in boxes and ready to go. They just need to be put in a truck and unloaded somewhere else. For a simple move, I don’t think it’s unreasonable to ask a good friend to help out like that, if in fact the circumstances leading to not being there were unavoidable.
Ah, yeah, I know. Where is the confusion?
I misread your post. Read it as “good enough friend to volunteer you and yours.”
Fair enough, Clockwork!
BellRungBookShut-CandleSnuffed - what is this “simple move” of which you speak? I am unfamiliar with this animal.
I once moved from a one-bedroom apartment to the two-bedroom next door. Literally next door: same building, same floor, from 1206 to 1204. I hired a couple of homeless guys to carry my furniture from one apartment to the other, and my girlfriend and I carried the boxes of clothes and such. We’d also bought some new furniture and appliances, which were delivered by the store at which I was an appliance manager.
That was a simple move. I’m not sure there are many others.
Oh, and I bought the homeless guys pizza afterwards in addition to the money I promised them, and I paid 'em more than I’d promised because I was too lazy to go get change.
Dangerosa, I approve of your list. I move we send it to everyone we know, and tell them to send it to everyone they know. We’ll teach these bastards the etiquette of moving somehow, some way!
I’ve run into most of those moving family, too, which is why we’re so glad we’ve opted out of the reciprocal moving obligation by using movers for our last move. So long, suckers! 
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ETA: My dog typed that. Sorry! I don’t have any advice. She just wanted my chicken. 
Translation: Your friend’s girlfriend is a bitch.