Don't know if it's the worst, but four laps of climbing San Bruno Mountain with winds gusting up to 40mph was fun... For two of the laps, the wind was also blowing against me going down. Even in a tucked position, I could barely even reach 25mph (I normally can cruise down at ~40mph downhill w/o wind). I usually aim for 5 laps, but I felt that I'll fall over on the climbing part if I tried for the 5th lap...because my legs had no more strength...

Worst for commuting so far is wind blowing against me most of the way going to work and just about all the way coming home. The wind was coming toward me at the 10 o'clock position, which to me is worse than a direct hit because I have to keep correcting the steering-->also a bit more dangerous when you ride along with cars. Oh, BTW the winds were sustaining around 20mph with gusts up to 35mph.