Hm... I'd suppose on of the Xbox Halos, when my friends wrangled me into multiplayer. One of those games still holds one of the BEST moments in my multiplaying life (was I even playing that round?). It was a very open, box-shaped stage with a lot of walkways spanning the upward expanse, and from all the way at the bottom, one of my friends lobbed a sticky 'nad'* all the way onto my other friend on one of the higher walkways...right in the middle of his visor. That part of the screen was almost entirely glowy blue until it exploded.
*apostrophes for exclusions more than quotation