Actually, I've seen it (mayo) done throughout the benelux, can't swear to France - I tend to avoid it when possible.  Definitely the preference in Maastricht, ketchup receives strange looks.

Of course, it could be the coffee shop smoking clouds my perception.

Skunk, anyone?

Klebnor

Lotus 123 ~ S-Render ~ OS/2 WARP ~ IBM 8088 / 4.77 Mhz ~ Hercules Ultima graphics, Hitachi 10 MB HDD, 64K RAM, 12 in diagonal CRT Monitor (16 colors / 60 Hz refresh rate), 240 Watt PS, Dual 1.44 MB Floppies, 2 button mouse input device.  Beige horizontal case.  I don't display my unit.