Clue: Will they make smut, rude bits, blue gags, even some vile oath that isn't very nice? (4-6,5)
Answer: FOUR-LETTER WORDS
Explanation: Definition: Will they make smut, rude bits, blue gags, even some vile oath that isn't very nice?
Every word in the clue is an example of one, and the whole clue defines them, so &lit. Excellent