Here's a couple different ones:
The Silencer walks into a room. All 50 enemies in this room rush towards the Silencer and surprisingly to their deaths(well surprising to them . . . the Silencer knows better.) After killing all the enemies, the Silencer walks across the room to the door opposite the one he entered. He turns around and takes off his helmet and says:
(In Urkel voice) "Did I do that?"
or:
The Silencer walks into a hallway filled with baddies who all ready themselves to try and best this mighty Silencer they have heard so many stories of slaughter about. Before attacking the Silencer reaches up and tries to remove his helmet.
The baddies in the hall all stand and stare at the mighty Silencer who is standing at the end of the hall fiddling with his helmet. After 5 or so minutes of fiddling the Silencer gives up on removing his helmet and just turns on the microphone switch on the side:
" (Squeal). . . is thing on? OK, Good. Well sorry guys I was going to give you a chance to look into the eyes of the one who kills you but my helmet seems to be stuck. Oh well."
He shrugs then readies his weapon. For the next 10 seconds he proceeds to make mince meat of all the baddies in the hall. He then walks down the hall and speaks no-more.
or much more simpler:
The Silencer walks into a bar filled people. With gun holstered the Silencer proceeds to sit down and take off HIS helmet. When the Silencer sees all the stunned faces HE says:
(in effeminate voice) "Not again Sam(us) Aran. Why does everyone think I must be a woman? Is it just because I'm in a suit with a helmet? Look people I slaughter people, not little bugs and bat like creatures. So what if she takes out a few large monsters, I've taken down a consortium."
(Alternately-same bar scene) The Silencer takes off HER helmet and says:
"That's right people, I'm a woman, Sam(us) isn't the only girl around town that knows how to use a weapon. And as for the rippled suit of armor? I find that a muscular physique helps instill the fear. Wouldn't you people agree?"
I hope to come up with more as I think about it longer. Also I like the library one but the book could be titled: The Idiot's Guide to Killing: Mercenary Edition.