Is that even a kink? Anyway, some character attempts to punish Rumlow by raping him or if not raping, then beating the hell out of him. The catch? Rumlow has a very strong masochistic streak and he thoroughly enjoys it. Maybe it was a kind of a sadistic game other HYDRA agents played on him and he got to love it?

+ Bonus points if his masochism is addressed by other characters in the fic
++ Even more bonus points if it's more than one person
+++ My spare trash can if it's one of the good guys from TWS