Pretty sure it's okay to link to the wiki since it's our bible: http://fallout.wikia.com/wiki/Charon_%28Fallout_3%29
Go to behind the scenes and it says "Charon tells you that he "finds happiness in a warm gun." - an allusion to the Beatles song "Happiness is a Warm Gun." " Which is more than cool and all but I've never heard him say that.
Does anyone know when that is?
I did a search but I got a load of pages about God and being happy... I svck at clear search terms.

I'm sure llama will come along in a lil bit and tell us the specifics but IIRC he says it when you change his tactics and tell him to use ranged weaponry.

Now I think about it, I should probably have gone straight to her XDD She's a goldmine for this stuff.

... as a side note: internets 4 you.

I think the Internet's trying to tell you something

OH NOES THE MACHINES ARE BECOMING SELF AWARE! :<
Seriously though. Nothing at all came up, except someone on a little known forum quoting it. :/

@ Bittercup,

Ghouls is right, he says that when you talk to him about using ranged weapons. The entire quote is, "If that is what you wish, then it is what I shall do. I must say, that I find happiness in a warm gun." If you go into the Tactics Menu and you are telling him to keep using Ranged Weapons and he says, "It is what you wish of me." Then go back out and tell him to use Melee Weapons and go back in and tell him to use ranged weapons and you'll get to the quote you're after. If he's already set to use Ranged Weapons when you try to get the quote out of him he won't say it.

Ahhh thank you. I think next time I will just ask you. XD I get my hopes up you see, thinking there might be ACTUAL DIALOGUE but alas, there is none. :'( Except for when he pretty much said '[censored] off and die' before I started the purifier. I coulda killed him. Thankies! <3

Edit: O_<

Ghouls knew the answer; I think she knows more about hanging around with Charon than I do. She's played the game more than I have and has travelled with him at least as much as I have and (again) probably more. I just muck about in the GECK with him so have lots more nerdy knowledge about him. And, ya, Charon has no ACTUAL DIALOGUE. The most he says is what you hear when you hire him. I mean, he has sentences when you talk to him in his menus, but that doesn't really count, does it? I used to listen to everything he said about Ahzrukhal every time I hired him when I played on the 360 just so I could actually hear his voice. And I guess he talks/yells a lot during combat. I modded him mostly because he is so quiet and so I could give him more to say.