This expression was often used in David Willis' comics by Joyce, an overly religious character uncomfortable with her own and other people's sexuality.
It can be used as a humorous reference to any form of extramarital sex, especially to mock people with attitudes similar to Joyce's.
Dave: "I thinkSam and Jenny finally got around to some P.M.H.P.
Giant magical flying cocoanut with hyper-sensitive solar powered mechanised baby firing meachnism and cancer injecting needle gun.(is to be said really fast...all at once without breathing)
Taco "what the hell is that"
Ryan "G.M.F.C.W.H.S.P.M.B.F.M.A.C.I.N.G"
Taco " a what O.o"
Ryan "a Giant magical flying cocoanut with hyper-sensitive solar powered mechanised baby firing meachnism and cancer injecting needle gun"
Giant magical flying cocoanut with hyper-sensitive solar powered mechanised baby firing mechanism and cancer injecting needle gun.(is to be said really fast...all at once without breathing)
Taco "what the hell is that"
Ryan "G.M.F.C.W.H.S.P.M.B.F.M.A.C.I.N.G"
Taco " a what O.o"
Ryan "a Giant magical flying cocoanut with hyper-sensitive solar powered mechanised baby firing mechanism and cancer injecting needle gun"