It's happened to all of us, a friend's over or near you, and you do something incredible right when your friend stops watching/goes away and calls your story a bluff/not as cool as it really was.
So tell stories of times this happened to you in a game.
Mine:
I was playing TF2, as a spy, I wasn't doing so good, I had much more deaths than kills, my brother was watching at the time, so he goes to the bathroom and I turn a corner and see 5 people with their backs to me, so I managed to kill all of them and right as the last person dies (Which my brother sees) he goes "Wow so you finally got a decent kill?" and I try explaining to him how lucky I just got and he just shrugged it off like I was lying.