English Expression: Keep it between the mayonnaise and the mustard
It’s Christmas time, and many people are getting home late from Christmas parties.
Remember if you drink DO NOT DRIVE!
Make sure you have a designated driver before you get lit up like a Christmas tree.
If you are a designated driver you will probably be driving late at night, so please slow down and keep it between the mayonnaise and the mustard.
Incidentally, mayonnaise refers to the white edge line on a road and mustard refers to the yellow centre lines.
If you keep your car between these two lines, you will be fine, if you go over either of these lines, then you could be in a world of hurt.