He who sups with the devil should have a long spoon

Possible interpretation: If you eat with the devil, you need a (very) long spoon so that you can keep your distance. If you mix with bad people, you should be careful not to be influenced by them. A warning not to get too close when dealing with evil people.

Note: sup (verb) = eat supper ("supper" is an evening meal) | the devil (noun) = (in Jewish and Christian belief) the chief evil spirit; Satan | spoon (noun) = an implement consisting of a small, shallow bowl on a long handle, used for eating | The phrase "to sup with a long spoon" (or similar) is often used alone, with no reference to the devil.