Many to choose from, including a few recent ones:
2001 Snow Bowl vs. Raiders - driving home in blizzard conditions with no roads plowed & everyone in the car with me passed out from drinking, brutal (but we won, so easier to take!)
2002 Home opener vs. Pittsburgh, opening of new Gillette Stadium. Brutally hot, like 95 degrees and I was 7 mos. pregnant with twins, but no way I am missing the opening of the new stadium! Drank lots of water and had to pee multiple times during game. Hit fans in front of me with my stomach. They were probably mad or uncomfortable, but I was psyched! Famous for Pats's stadium guys playing Kordell Stewart clip from prior year's AFC Championship Game where he said, "sometimes the best team doesn't win," over and over again as the Pats wiped the field with the Steelers again. BB was mad about the clip, but it made the crowd roar every time! And we won!
2003 Miami game (12/7/03) - snowing all the way to the stadium; neither parking lots nor stadium plowed, had to dig out your seat yourself; famous game where Tedi Bruschi intercepted the ball on like the 10 yard line and ran it in for a TD. Fans threw snow in time with "Hey" song. Fun except for drive on way down; snow stopped during game. Pats won 12-0!
2003 Titans playoff game - so cold the chili we brought got stone cold going from the bowl to your mouth on the spoon; hubby lit gloves on fire over portable fire pit trying to keep hands warm; adapter from crockpot (to keep chili warm) blew out lighter/port in car; brutal (but we won, so easier to take!).
12/16/12 Pats v. the 49ers. Cold and pouring rain for the whole game, which was at night. My daughter's feet were cold and wet and she was crying, so I had to give her my warm Uggs and the Pats socks I had just purchased for my son at the Pro Shop. And the Pats were getting killed. One of the few games I can remember where we left pretty early (like at half-time). Just miserable (and the Pats almost came back, but fell short at the end).
09/24/17 Pats v. Houston Texans - brutally hot (hottest game I think I have ever been to, with sun beating down mercilessly on most of the stadium). Gillette ran out of bottled water and charged fans $4.50 for cups of tap water. Nice PR move, Krafts. But, you guessed it, we won! and that leads to the other extreme:
12/31/17 Pats v. Jets. Brutally cold (apparently the coldest Patriots regular season game on record). Had several of my kids and friends with me and nobody could stand sitting in the upper deck. But...we won!
Cold rain is the most miserable of weather conditions so there are many runners-up, including the Browns and Dallas games this year (Dallas was a rare miss for me, and as I watched it on TV, I was glad I wasn't there).
Pats usually win, and the walk back to the car is always shorter after a win!