The most common and most likely answer to this crossword clue is the 2 plus 6 letter word NO THANKS
I've seen this crossword clue in The Guardian
N
O
T
H
A
N
K
S
Buddy explains!
The straight part
We know that "I don’t want them!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case i don’t want them! = no thanks.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.