Every course on WGT has at least one hole to offer that I loathe, though the order changes from time to time. Oakmont definitely is worst...no matter which hole, as soon as you don't hit the fairway you're going to be in BIG trouble.
The holes I hate the most:
Oakmont #9: Very long, and a treacherous green as well. Usually I aim my approach shot at the bunker and try to stick the bunker shot near to the pin. Seems a more reliable option than playing a long downhill putt with evil breaks as well.
Bethpage Black #15: I aim the approach shot to the bottom left corner of the green and hope the backspin will carry it back to the pin. Often the approach gets stuck in the rough, calling for a pitch or similar shot. If that doesn't end up close there's little chance in making a par on this one.
Kiawah #5: Most people hate #17 or #14, but in comparison I find #5 much harder (all par 3s, by the way!). Especially with a strong wind behind you I find it almost impossible to make the ball sit near the pin.
St. Andrews #17: I've been playing this hole much better recently, but it's still a challenging one...