Is having sex with this humptastic clone of yours an act of gay sex, or an insane new form of masturbation?
It's hard to imagine sex with another person as masturbation, but is this even another person? Genetically speaking, this is you. On the other hand, you and your clone are the same sex, so clearly this is at least gay, right?
The correct answer is, of course: gay. Your clone may be genetically you, but it's still a separate entity. If you die, the clone lives on, complete with memories of the strange gay sex session the two of you had just after your clone was born. How that will ruin their psyche, we can only speculate.
Now for a twist! Shyamalan!
Not the Sixth Sense kind where the clone's dead, because even hypothetical necrophilia is goddamn disgusting.
An alternate version of this hypothetical posits not a clone, but a time traveler. You have gone back in time -- let's say to last week -- to warn your past self that you're about to get good and sexed by future you. Is this sexual encounter gay or masturbation? Contrary to what your first instincts may tell you, this is not the same as the clone scenario, and is 100-percent not gay. This is meta-masturbation. Masturbation involves pleasing oneself, while a gay encounter requires another member of the same sex. Past You is not another member of the same sex per se; it's the same member. It's you, pleasing yourself (assuming you don't do it wrong), and therefore crazy sci-fi masturbation!
Or crazy sci-fi awkward small talk, once you see what you actually look like and gag uncontrollably.