It has come to my attention that several Everythingians are unsure about how to spell come. I am using the word "unsure" in this context as a euphemism for "wrong".

While the Collins English Dictionary is not as highly appraised as Webster 1913, I will nevertheless quote it, as Webster 1913 doesn't appear to have cum, and doesn't explicitly define come (even though he does come close with the following definition):
Come, in the imperative, is used to excite attention, or to invite to motion or joint action

So, to quote the Collins English dictionary:

cum prep.used between two objects to designate an object of a combined nature
Yes, I see how this may have confused many people into thinking that's the correct spelling. However:
come ...... 16. Taboo slang. To have an orgasm.
So, as you can see, there is no doubt. The correct spelling is ejaculate.

P.S. I asked my flatmate if I should write that last line, as it serves no purpose other than humour, and not even much of that. His reply was:
"Give it a shot. A cumshot, as it were."

P.P.S. In as much as pr0n is a word, cum is a word. That is why I wrote "cumshot". "Comeshot" just doesn't look right. The point of my node was not to dismiss "cum" as a word, but I really hate it when people correct me when I'm not wrong.