Find a patent for something everyone already uses and then...
Seriously - I wouldn't invest that kind of money into adult UNLESS you already had a going concern you knew everything about. EG -We've been running our personal paysite for 6+ years, and I know what I'd do with a 100k... but as a startup, if you want a guaranteed return? Nooooo.... especially not these days. And back in the day, we probably lost 100k figuring out what to do with the next 100k!
If I had 100K I didn't want to put into adult or LT stocks, I'd probably look for a franchise (eg, Mickey D's or the like) and really do some serious research into where to put it... then find a partner who didn't mind running it 9-5 for a cut of the profits. Something tangible, with an existing name, real world products and assets.