The five-time major champion issued the trash talk Thursday on Twitter.
"This is going to be the first time in a long time that I've used two drivers," Mickelson said. "As if one [Callaway] Epic Flash driver isn't enough, I'm going to use two. Well, why such a change of heart? Why am I doing this?
"Well I saw a post of Bubba Watson hitting bombs without a shirt on and he had bear chest hair. And I don't mean b-a-r-e chest hair, I mean grizzly bear chest hair. I thought, if I have to have that to hit bombs, I don't want to hit bombs."
Mickelson is using the strategy at the 2019 Memorial Tournament, a precursor to the U.S. Open. The Memorial Tournament began Thursday in Dublin, Ohio.
"Lefty" said he has a shorter drive to hit "cute little cuts into the fairway." But he also realized when he wasn't hitting bombs, his confidence was low.
"When I started hitting bombs, my confidence shot back up, my testosterone came back, my overall attractiveness increased," Mickelson said.
Mickelson said he plans to take two drivers with him to the U.S. Open, one to hit "cute little cuts" into the fairway and another to "hit bombs."
The veteran golfer was referencing a video Watson posted on May 13. He filmed himself using a golf swing simulator, while shirtless.
"Phil Mickelson, you do have pretty calves, but you don't hit the high bomb," Watson said. "People want to see the glutes, man."
Watson is ranked No. 18 in the world, while Mickelson sits at No. 23 in the rankings. Neither golfer has won a U.S. Open title. The 2019 U.S. Open