From the little we see in "The Force Awakens," Kylo Ren and General Hux have a tense professional relationship as they are both competing for Snoke's respect (or Snoke's hologram's respect). Some fans have read sexual chemistry in this tension -- don't act surprised! Kylo and Hux are two attractive young bad boys (they're the Finn and Poe of the Dark Side), and the internet is the internet. Climb aboard on the Kylux ship and never look back.
You know you raised your hand...
The fan art in the thumbnail is by I3ear-fat
The tweet is by @radartech_matt