The most common and most likely answer to this crossword clue is the 6 letter word RATBAG
I've seen this crossword clue in The Guardian
R
A
T
B
A
G
Buddy explains!

The straight part
We know that "Creep" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case creep = ratbag.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does RATBAG mean?
RATBAG noun- A despicable person.
- (sometimes affectionate) A mischievous person, especially a child.