SUDDENLY, DICKS MISSING EVERYWHERE.
Perhaps it was a brain-addled scientist-cum-splicer that triggered an accident in the labs, something else but pheromones being filtered into the city and their supply of ADAM, or a mysterious fortune cookie, or a handy magic stone brought by an uncle from India, or some strange quirk in the universe, but today...
Today you wake up and something isn't quite right...
HOW IT WORKS!
Pokémon's done it, X-Men's done it, and so has pretty much every long-running television series, comic, etc. In fact the trope has become known as the "Freaky Friday Flip" (WARNING: LINKS TO TV TROPES!) from the popular remake about a daughter and mother switching bodies.
Your character is genuinely swapping bodies (or minds, however you look at it) with another character. They will look and sound exactly like that person, although their personalities, inflections, dialects will stay the same - if they so choose. The fun part is that only you know who your character really is, unless they choose to disclose to someone or in public.
Thus, hilarity (or chaos) ensues.
All you need to do is borrow (or make) a few icons of your swappee/swapper/whatever and get posting. As with the last event, the effect extends to the meme as well so long as you post in-character.
HAPPY SWAPPING!
You'll have an easier time remembering to be someone else if you change your default.
If you've reached your userpic limit, save and delete some of your icons until the event is over.