Apologies for my absence, chaps and chapesses. Have been a little busy with the nice people at the Oakley store here in Boston. They have relieved me of some pecuniary funds. 8)
Anyway, on the topic of jacket and jeans. If said jeans are pantalons de Nimes, then the answer is, quite simply, no. It’s in the Manifesto! You may wear any number of things atop pantalons de Nimes, but a “sports” jacket, as our American cousins would term it, is a big fat screaming pile of “NO”. To see why, simply look at Clarkson, as already described by others.
If, however, your jeans are more of this line; ]
http://www.orvis.co.uk/store/product.aspx?pf_id=34HX&dir_id=466&group_id=481&cat_id=7432&subcat_id=7433 (Orvis KHPs, as worn by yours truly today) then I would say a decent tweed jacket would work rather well. I’ve been known to sport my hacking jacket with these. Along with an open knecked shirt and some decent boots.