devil of it

[devil of it] or [heck of it] {n. phr.} 1. The worst or most unlucky thing about a trouble or accident; the part that is most regrettable.

Andy lost his notebook, and the devil of it was that the notebook contained all his homework for the coming week.

When I had a flat tire, the devil of it was that my spare tire was flat too.

2. Fun from doing mischief. - Used after "for".

The boys carried away Miss White's front gate just for the devil of it.