I think with being the silent type he'll randomly burst into a cheesy mid 90s song upon taking his helmet off when he sneaks up behind someone...

"Shhhh Shhhh
It's, oh, so quiet
Shhhh Shhhh
It's, oh, so still
Shhhh Shhhh
You're all alone
Shhh Shhh
And so peaceful until...

You fall in love
Zing boom
The sky up above
Zing boom
Is caving in
Wow bam
You've never been so nuts about a guy
You wanna laugh you wanna cry
You cross your heart and hope to die
Til it's over and then
It Will be when I count to ten
one,two (fires gun) ten

Then he will shoot said poor person about 25 times, Though the pain from the 30 seconds of singing is probably far greater and death would have been a salvation at this pount.

"Ok, that's how I get the helmet off. Now, how do I get these leggings off? I've needed to pee for years and I'm so mad about it that I just keep killing people."

Already got it, both physical and GOG.
So i'm not entering. Just here to say, i approve this contest.
The Silencer sat on the couch, took of his helmet and asked
- Hon, what time does "I, Crusader" start?

"Gentlemen."
"THAT SILENCER IS A SPY!"

"Do I get paid now?"

*takes off helmet*

"I gotta go polish this thing again"

Have another.

*to the total surprise of his enemies the Crusader triggers his advanced tactical suite to allow for removing his helmet*

'Fool me once, shame on your bodies. Fool me twice, ... you won't fool me a second time.
Hasta la vista, WEC.'

*the Crusader fastens his helmet again and readies his rifle, causing a little panic in the room*

"We're no strangers to love. You know the rules and so do I. A full commitment's what I'm thinking of. You wouldn't get this from any other guy..."

Takes off helmet, smells inside of it

*sniff* *sniff*
"Damn, I need to remember to wash this thing."

(Takes off helmet. Gives long, cold stare)

MY TINKLE FEELS FUNNY
MOMMY I WANT A POPSICLE
WHAT IS THAT????

(Puts on helmet, continues shooting)

"Where can I find Uwe Boll and Michael Bay?"

I almost spit my drink.

Apparently I have to write something because GOG won't allow me to post with a simple ;P

He would say :
"Hey I am Vagabond, and I'm a bitch for not telling Emualynk there was a signed LP of Machinarium OST available.
I have remorses now!"

He would then proceed to do hara kiri to himself since the title of the game is lying.