Popular opinion is your query letter subject line should go:
TITLE – genre
I used the genre in my subject line only once. It was for a script that had an innocuously sexual title. I added the genre to qualify the email as something other than spam which is how it might have otherwise appeared.
But let’s not mince words here. This is what you’re doing. Targeted spamming. So I’d be very careful not to fall prey to any sleazy tactics in your subject line. Don’t resort to trickery or being clever. If you’ve got an intriguing, evocative title then that should be enough.
Also realize that certain email handlers (Gmail for one) give the recipient a preview of the email in the subject line space. So watch out of redundancies.