One Classic 40K moment I have never forgotten was in a game with my mate Glenn with his Orks Vs my Black Templars.
Well Glen had scratch built this huge Ork truck that could actually carry 20 Ork Boys &l this was its first game. He had it on the far left flank of his deployment Zone waiting to rush forward.
I had gotten the first turn & I fired at it with a Las Cannon armed Templar on a hill with clear line of sight. It hit, I rolled & penetrated. Rolled a 6 , Exploded & he lost 75% of the squad from bad saves.
You should have seen his face!
We still laugh about it now & he sees the funny side. He is always great fun to play against!