The most common and most likely answer to this crossword clue is the 10 letter word SIXTY-NINE
I've seen this crossword clue in The Guardian
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Buddy explains!

The straight part
We know that "Oddly sexy, innit" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case oddly sexy, innit = sixty-nine.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.
Crossword Answer definitions
SIXTY-NINE noun- The cardinal number following sixty-eight and preceding seventy.
- (sexuality) A sex position where two people give each other oral sex at the same time.
- To have sex in the sixty-nine position: to engage in mutual oral sex.