The infamous catchphrase used by in my opinion one of the best Youtubers ever, SSoHPKC, or also less commonly known as Seamus O'Doherty (yes, that is very irish. :) ). It has been used on multiple occasions, such as in Seamus's |Famous| Fallout 3 playthrough, I believe it was Mothership Zeta, titled shotgun rain in space if you wish to find it, however its been a while, so it may not be that exact video. It has also been used in his |Semi Famous| Mafia2 playthrough (btw, when i say 'Famous' i mean famous on his channel) in just about every video there since the variety of weapons in that game is not very large, so Seamus found himself using 'Shotgun Rain' quite a bit. You may still be asking yourself what does it mean though? It means when Seamus blew someones fucking brains out with a shotgun and then yells 'SHOTGUN RAIN!!!' This has to be his #1 catchphrase, along with 'Kennyed' (which would be #2. It has also been used in the dupstep song for SSoHPKC (which was my personal favorite) Or rather, SSoHPKCstep.
SSoHPKC:Shotgun rain... another alien takes the lincoln Train... Shotgun Rain... Cmon... C'mere alien, I got something right here for ya... right-- WUB WUB WUB WUB HERE! RIGHT, HERE, RIGHT, HERE!!! WUB WUB WUB WUB!!!!