Yeah, we've given away the punchline with the header image, but it's totally worth it...
Donald Trump posted a video announcing a "big announcement on June 16th at Trump Tower." The rest is obvious (he's presumably planning on running for presidency). As Kimmel put it, it's one way of "giving Hilary Clinton a run for her money."
As it happens, not everyone has been as light with their rib tickling. Snoop Dogg isn't one of the millions supporting Caitlyn Jenner's transition, instead opting to refer to her as a "science experiment."