Loktar, that was not an answer!
Well, Gagh, Dr. Pepper has, as you surely already suspected, a secret ingredient. (Some still say it is plum juice, but we all know that this myth was created by Charles Alderton himself to distract from the fact that the plant extract he used was not entirely legal even back then.) Anyway, when Dr. Pepper was first filled in bottles, plastic was a long way from being invented, so nobody could anticipate the strange but chemically quite interesting reaction between the secret ingredient (not plum juice) and the estrogen residue in PET bottles. While of course COMPLETELY AND TOTALLY HARMLESS, the resulting estrogen derivate sends out a pheromonic message along the lines of 'go fuck the next man you can get', thus making it a really welcome party drink in certain circles - unfortunately though, to some men completely not gay and totally into women, the substance would be detected by their gonads and immediately translated into a decrease in taste that would result in said male's rejection of any further Dr Pepper.