good question!
I guess it would depend on several different things, Simon's motives, whether or not he in fact knew it was himself, where he came from to begin with. If, say, Simon had been fished out of some alternate universe and was brought here then thinking time-line wise the ice king wouldn't be him so much as things like his personality, appearance and powers have been changed by the ice crown, so an alternate Simon may not have been destined to become like that and therefore have little connection with the ice king, although going biologically in this instance we cannot tell how much the crown may have altered him. Yet also thinking time-line wise Simon may have been destined to go mad anyway, and a huge number of possibilities could also be true for where-ever this Simon had came from.
But if he was in fact from the same time-line then it may be a different case, seeing as he is almost doubtlessly going to become the ice king, you could argue that this encounter or another event could let him deviate from natural course but then he possibly wouldn't be from the same time-line in this case would he?
It also, I suppose, would depend on what agreement or non-agreement was between both parties, from this picture we can assume by the startled appearance of the ice king that perhaps he was unprepared for Simon's actions and because masturbation implies that as a whole they should be both pleasured or satisfied this may not be the case.
As for motives, if Simon were to do this because of opportunity, you don't meet your future self everyday, then we can guess that he probably isn't thinking about it in the same mind as someone in a gay situation might. Of course, this brings in the whole new thought of sexuality, because of Simon's relationship with Betty, if he were to be strictly homosexual that would probably make him a closet homosexual, either afraid to admit or unknowing of it. This could give him completely new reasons to be kissing himself. I haven't even started discussing the Ice king's opinions.
tl;dr, I am using your simple and humorously implied comment to ramble please ignore me, this probably doesn't even make sense.
I guess it would depend on several different things, Simon's motives, whether or not he in fact knew it was himself, where he came from to begin with. If, say, Simon had been fished out of some alternate universe and was brought here then thinking time-line wise the ice king wouldn't be him so much as things like his personality, appearance and powers have been changed by the ice crown, so an alternate Simon may not have been destined to become like that and therefore have little connection with the ice king, although going biologically in this instance we cannot tell how much the crown may have altered him. Yet also thinking time-line wise Simon may have been destined to go mad anyway, and a huge number of possibilities could also be true for where-ever this Simon had came from.
But if he was in fact from the same time-line then it may be a different case, seeing as he is almost doubtlessly going to become the ice king, you could argue that this encounter or another event could let him deviate from natural course but then he possibly wouldn't be from the same time-line in this case would he?
It also, I suppose, would depend on what agreement or non-agreement was between both parties, from this picture we can assume by the startled appearance of the ice king that perhaps he was unprepared for Simon's actions and because masturbation implies that as a whole they should be both pleasured or satisfied this may not be the case.
As for motives, if Simon were to do this because of opportunity, you don't meet your future self everyday, then we can guess that he probably isn't thinking about it in the same mind as someone in a gay situation might. Of course, this brings in the whole new thought of sexuality, because of Simon's relationship with Betty, if he were to be strictly homosexual that would probably make him a closet homosexual, either afraid to admit or unknowing of it. This could give him completely new reasons to be kissing himself. I haven't even started discussing the Ice king's opinions.
tl;dr, I am using your simple and humorously implied comment to ramble please ignore me, this probably doesn't even make sense.
Your rambling is awesome.
Thanks! It's good to know it's at least legible. 
Well, noting that the Ice King responds positively to essentially any expression of love or even attention (Finn's kiss on his cheek, for example), we could guess that his fractured mind is beyond the boundaries of his previous sexual orientation, whatever it may have been. However, this may not be conclusive as we still do not know what Simon's sexual preferences were. Simon himself does not appear to have begun his transformation yet; therefore it is implied that he has no awareness of this blue, bearded kissing partner in fact being his own future self. Taking this into account, one can safely assume that he thought of the Ice King as another person, and therefore would require consent in order to perform any act of this nature on him. This would mean that he must have simply found the Ice King attractive enough that his focus on that overcame his attention to the proper kissing-related etiquette, and beyond that, the fact that this would arguably constitute an infidelity towards his fiancé.
you sir are absolutely brilliant.
D You too!
It made sense to me! 