If you're not seeing this feature in your Facebook account (in Ads Manager or Power Editor) it's possible that facebook hasn't rolled out this feature yet in your country. They roll out features on a country by country basis but typically start in the UK or USA in my experience. What country are you in?

I could propose a non-Facebook alternative for the tall clothing niche, in case you're interested. Send me message, and I'll explain.

Hey there,

Facebook ad targeting options are always changing, so it's possible that they've removed that Behavior option for a variety of lessons.

The easiest way to substitute this functionality would be to use Interests instead of Behaviors, and go after fans of Big & Tall, Casual Male XL, and other similar retail stores.

If it's helpful, we've put together a complete guide on every Facebook Ad Targeting option currently available at http://www.contentharmony.com/blog/facebook-ad-targeting/ . This page is easier to search than hunting through the entire Facebook ad interface.

Good luck!