Similar incident happened to me when I lived in the dorms at my school
Came home from a weekend visiting my GF at her place fairly early on Sunday one weekend. Walked into my room to see my bed pushed against my roommate's turning two single beds into one queen (or thereabouts) with miscellaneous sheets, pillows, of both of ours on this amalgamated monstrosity. A few "hmm, oh..., OH!" moments later I came to realize the horrible truth about what went on when I went to visit my GF and my roommate had his over.
I just sat on the giant love bed until the two of them came back to the room then politely asked the both of them to never, ever, do that again and to please wash my sheets for me.