Show people with terminal conditions just how curable it will be not too long after they die.
That is EVILLLLLY funny! 
Isn’t it simpler just to talk the couple into an abortion? You don’t get no myrrh, maybe, but still…
Nah, just tell Joseph that no matter what Mary said you don’t want to abandon your son just to cover up your affair. After he’s completely convinced in your fatherhood, that’s when you abandon them.
You want to hang out in a dump like Bethlehem for some tainted frankincense and a tub of probably rancid myrrh? Now if it turns out Mary is smokin’ hot, that’s one thing, because there’s gonna be some “anointing” opportunities, if you catch my drift!
Or at least treatable. And while you’re at it, leave Freddy Mercury a copy of a Queen with Paul Rodgers performance.
Come to think of it, there are probably lots of artists/performers that would just hate to see how corporate interests use their work after they die.
Show Van Gogh how many other people will profit from his work.
You seem to be assuming that Newton’s lifelong virginity stemmed from a fear of women rather than contempt of same. I have reason to doubt that.
You people are all much more inventive than I am. All I could think of was to go tie together the shoe laces (or sandal laces) of people giving famous speeches while they’re speaking.
That makes it all the more evil, Skald. Whether he actually likes women or not is irrelevant.
Actually, now that I think of it, who’s to say some time-traveling asshole didn’t rape him with hookerbots, mentally scarring him for life? Hmmm…
Seduce Mary, videotape it.
When the SANTA MARIA arrives in 1492, there would be large signs on the beach “Last rest stop before China 10,000 miles to go.”
What would be the point? No one today has the slightest idea what Mary looked like, other than that she was female, probably under 18, and almost certainly not blonde.
Man, Hypno Toad brought his A game to this one.
Then how about this one: go back in time to a bunch of lily-white WASPs, prove that you’re from the future, and then tell people all sorts of stuff about the second coming of Christ that you know will piss them off:
-Jesus not only doesn’t speak English, but he himself pronounces it “Hay-zoos.”
-Gay is OK, but ONLY if they’re married to each other.
-Communion can be performed with any kind of alcohol, so long as it is at least 25 proof.
Or, “Occupado.”
Besides all this, give them really bad investment advice that will end up making them homeless and prostituting themselves for food.
Flying Spaghetti Monster cave paintings.
Go back in time to see what Jesus looks like, go forward in time to dig up a dead guy that looks like him, bring the dead guy back into the cave so when the stone is moved, there’s a body in there. End of Christianity.
Go back in time and steal the meteroite that becomes the “black stone.” End of Islam.
Oh wait, being a dick, hang on.
Modify tenents of Christianity to enable endless bloody wars with Islam. Sell weapons to both sides.
(besides robbing banks right before the banks are about to be robbed, leaving 10% for the criminals)
Sorry, but the black stone was there before Muhammed received the call to prophecy. It did figure in his life when he helped find a fair solution to which tribe had the honor of helping to re-enshrine it after some renovations in Mecca, but it’s absence (butterfly effect, butterfly effect, yeah) probably wouldn’t mess things up too much.