Possible meaning:
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.
Who said he who sups with the devil should have a long spoon?
This expression was in use in the 14th century and can be found in "The Squire's Tale", one of Chaucer's Canterbury Tales (c1386).
What does he who sups with the devil should have a long spoon mean?
Proverbial saying, late 14th century, meaning that one should be cautious when dealing with dangerous persons.
