Ugh, I hate like all status ailments so much, so it's hard to choose between them. Freeze is probably the one I hate the least, since I always seem to break out of it right away, and it's not one I see that often. Infatuation never really bugged me either, because usually I'm still able to attack like 80% of the time.
I'd say i hate Poison, Confusion and Sleep equally, because they're all just so goddang annoying. Poison not only affects you each turn in-battle, but slowly drains the life away from your Pokémon outside of battle if they aren't healed, and I usually never heal them.
I never seem to be able to hit when confused, and one time I didn't hit once with one of my Pokémon because of the stupid confusion, and it's especially annoying in battles that are already tough. Getting confused with Swagger though never appears to be a problem, and I'm usually able to hit, which helped me a lot while beating the Pokémon league in Sapphire no too long ago xD
I just genuinely hate Sleep. It comes at the worst times, and except for the first generation where you had the PokéFlute, I just never have anything to help me against it with me, so I'm usually stuck trying to wake up my Pokémon throughout the whole battle against Pokémon with one of those moves.