Fans hating on certain Pokemon/gens/whatever for the sake of hating them does offend me in a way. There's no basis for hating stuff without a legitimate reason, so it's a bit irritating when people complain about this Pokemon when they just say the most superficial reasons, which really tell me that they just simply don't like it. If they don't like it, well, that's cool, but if they start bashing it, that gets on my nerves.
I really don't give a damn if they're listing valid reasons to explain why they don't like it, but if they're just saying that it's awful for no good reason, then I might argue a bit. It doesn't bother me all that much.