The Watcher Watched
Fill for this prompt http://frostironkink.tumblr.com/post/148680852256/prompt-loki-was-always-masochist-but-there-is:
Loki was always masochist, but there is no such concept as BDSM in Asgard and everything percieve “weak” are scorned, so he never got any good experiences. Even the nicest people he found (in disguises mostly) treated him like useless shit. Now Loki repressing his needs as best as he can, pretending to be Odin and checking Midgard from time to time - he have plans for Avengers fighting Thanos. And “Civil War” clusterfuck was entertaining.
One day he sees Tony in BDSM session with some person (since he and Pepper broke up, Tony decided that “just for sex” friends are better than one night stands or something). And at first Loki just looks because Tony is inventive in bedroom as much as in the shop, but after he stunned by tender aftercare and the way Tony is stil polite and friendly to his sub after. Now Loki just HAVE to know more and get some of that for himself.