I was just reading about a guy who was in the Guinness Book of Records for having the world's largest Dalek collection, and my first thought was "I bet he just mentioned to some friends one day that he liked Daleks, and it just stuck."
It's inevitable really. Let it ever be known that you have an interest in a particular thing, be it Daleks or cheese-graters, and immediately everyone will sieze on it and assume that this is your thing. Every birthday, x-mas, or other gift-related occasion will bring more of the sodding things because it saves anyone from making any effort to think about what you might like. It's one step up from the completely random generic present, and it does give the illusion that they actually put some effort into getting something you might like, but actually it just means that they grabbed the first Dalek (or cheese-grater) related thing they saw and called it done.
And the trouble is that once it starts it's almost impossible to stop. Even a person who has no idea about your supposed cheese-grater obsession will assume it's your thing as soon as they see the shelf full of the damn things that others have already stuck you with. And you can't just throw them out because then you'd be hurting the feelings of the friends who put all that effort into bringing you back that Dalek-shaped cheese-grater from their holiday in Wales, and before you know it, you're in the Guinness Book of Records and you can barely move for colourful and oddly shaped, novelty cheese graters from the far corners of the world.
No, the only way to stop yourself being forever saddled with the unwanted obsession is to kill it before it takes root. Your best bet is to somehow link the despised object with some tragedy: "I can't even look at a cheese-grater since my pet rabbit died." not only makes anyone who attempts to give you yet another tawdry variation on the theme feel guilty about opening old wounds, but gives you an excuse to be rid of those which you have already accumulated.
Either that, or let it be known that you are into something so obscure (or expensive) that it defeats the laziness factor by requiring more effort on the part of the gift-giver than a regular present. I mean everyone knows I'm a big fan of Doctor Light, but I've already got both action figures that were made of her and the trading card. At this point the only option is hunting through back issue bins or searching online for comics that don't have her name in the title, and that's way too much like effort.