1. Everyone wants an A! If you get all A's it's been a fantastic Christmas or Birthday or whatever occasion you happen to have been showered in gifts. A gifts are awesome and you totally adore whatever the gift is. Either it's something you've always been wanting but haven't gotten around to buying for yourself, perhaps it's too expensive or you were just being lazy. Then there are the really neat gifts that you go crazy over and had no idea such a marvelous thing existed. So you could never have bought it for yourself as you didn't know about it.
2. B's are okay too. B's are okay because they turn into money. The B gifts are those that you don't want but they're still really awesome for someone and you can and do quickly sell them, thus getting yourself some cash to do with whatever you like. So in essence, whoever gave you the B gift gave you money. So... nice.
3. C gifts. These are okay in that while not as awesome as A gifts, things you want, or B gifts, things you can sell and thus buy things you want, C gifts can be useful to trade for things you want to friends if it's something neat they'd like but wouldn't specifically want to buy. They may not offer cash but may still hand over something of theirs that you like in exchange.
4. D gifts. Still not too bad. Those D gifts are okay. They save you money and trouble in the long run but otherwise don't directly benefit you like the A and B gifts. These D gifts are nice enough items to be saved and given away later to friends or family for gifts. Yes, the regifting. But it does save you time and money in the long run.
5. And finally the F gift. No one wants it. You don't want it. Your friends and family don't want it for a regift, and it just sucks so hard you don't even want to try selling it as it's just not worth it. So you trash it. It's just a thing no one wants so letting it go is the only thing to do.