My friend gave me the idea of this set. It does do a good job of annoying the opponent and can force a lot of switches. Here it is:

Grumpig, Thick Fat, leftovers, Calm, 252 HP, 156 Def, 100 Sp.D
Confuse Ray
Thunder Wave
Extrasensory
Power Gem/Shadow ball (I need a little help with this last move)
Yeah, this set is a little different from most grumpig set's you might have seen, but it is very effective at annoying the opponent. Simple little strategy here, just confuse ray as soon as you get in, t-wave the next (They might switch but it doesn't really matter), and if they did switch confuse again. Then start attacking with extrasensory which adds on a flinch rate. Combine all the hax's together, and your opponent has a 27/80 (Or 33.75%) chance of attacking. You can opt to go with a careful nature and switch extrasensory to zen headbutt for better hax rate (24/80 or 30% chance of attacking), but grumpig's attack stat is so crappy compared to it's special attack that I would go with extrasensory. The last slot is hard, but power gem gives a broader type coverage for grumpig, where shadow ball is a little bit more powerfull but doesn't give much out of psychic's and ghosts. Shadow ball also means dark types can come in and take little damage from this set.
It's also good to have spikes and stealth rock support along grumpig, because this grumpig should will force a lot of switches. This means you should have a ghost on your team to stop an opposing rapid spinner, like mismagius, to keep those rocks and spikes up. This grumpig is made very bulky, and with thick fat, switching in on fire and ice attacks is easy. 252 HP is obvious, and i split the rest of the EV's in both defense's just so it can handle attacks from both sides of the attacking spectrum.
Anyways, it's a little different from most grumpig you've seen (If you've seen any due to it being so underused), but if you like haxing your opponent to death, gathering up damage from SR and spikes, and kicking ass with a pig, then this Grumpig is for you. Please comment and leave any ideas. Thank you.