My recommendation is the messenger bag from Vanguard called The Heralder. I use the largest variant with my 1D-X plus 3 lenses and a laptop or better an iPad. It does not scream "camera bag" and you can bring it as a laptop bag to strict business meetings without anyone raising an eyebrow. Apart from that I agree with Paul Walnut that the camera bag from Jack Wolfskin merits a recommendation, but this is a backpack, not a messenger bag.