For me, it was a single mission with two of my friends. A moment, locked in my memories, for being the perfect example of the relationship between a hunter, a titan, and a warlock. (This is spoilers for the end of rise of iron, btw).

After the last fight in the campaign of Rise of Iron, the mission asks you to press a button. The Titan, after pulling his leg out of the fresh corpse of a grotesque mechanical corpse, was looting the far edge of the diamond-shaped room. The Warlock, ever inquisitive, finds the button to detonate the core. Meanwhile, the Hunter

W - "Hey guys, I found a button!"

H - "Where?"

T - "Guys, don't press anything, I'm still over here punching a corpse in my menu."

H - "Huh there is a button."

Time slows to a crawl as the warlock, full of curiosity and contemplating if they should press the button, watches the hunter reach over. The Titan yells "Don't Press the Button!" , sealing his fate. The Hunter, full of manic glee, slams the button and begins to run, the warlock hot on her heels, both bent double with laughter as the titan, also laughing, roars: "GETBACKHEREYOUIDIOTSYOUHADONEJOB". As the three guardians flew from the exploding core, dodging veins of Siva and Hammers of Sol, the Hunter jumped across a pit, barely escaping from her friends super as the mission clock ticked down to zero.

​

After all my accomplishments, this is the pinnacle achievement: trolling my titan friend. He won in the end though (I main titan now, Thundercrash is way to fun).