Frienicator

A relationship between two people who are friends, but occasionally take to doing the nasty.

A variation on the not-so-pleasant sounding classic, "fuck-buddy" or the new wave "Fornifriend".

Bob kept trying to explain to Ted that he and Mary were NOT in a relationship. There were no dinners bought or gifts exchanged (other than bodily fluids). They were frienicators and it was a simple case of frienication.