Help..how do you wear jeans...

You're gonna need to dress it down. Best way is with some boot cut jeans and cowboy boots or chelsea boots. Underneath you could wear a t-shirt or an button-down open at the collar. It's hard to tell exactly though cause I don't know what type of tux jacket; for this post I'm assuming it's SB.

Maybe you could do the Hedi Slimane/Tom Ford thing, and where it with a plain white shirt open at the collar (Hedi Slimane wears a t-shirt underneath, Tom Ford not), or tux-style shirt with the cuffs undone, and dark, slim, boot cut jeans, as Mike C suggested. I think that for this look to work, both the shirt and jacket need to be quite fitted. It also helps if you are stick thin. I might accessorize with a pair of dark framed glasses, to complement the darkness of the jacket, and give the whole thing a bit of underground aspect.

Yea, that would work, but I don't think it's gonna be as casual as you would like (ie, just walking around shopping or for daytime wear).

I guess that what you suggest would work, although I generally think of loafers with jeans as sort of an older guy thing. I would definitely second the Chelsea boot idea. I know that a lot of ad and editorial pages have been devoted to the former, but I've yet anyone under white guy under forty emulate this look successfully, although I have seen a few young black guys do it. I think the problem with pairing loafers with jeans is that jeans are associated with workwear on this side of the Altantic and in Britain, whereas loafers are traditionally the footwear of leisure.. In Italy and France, where there is no such connotation, and where jeans are often cut more like slim trousers, you get a sort of louche, loungey feel.