This is a LEGO lenticular (NOT testicular) created by Arthur Gugick featuring Batman when viewed from one side, and the Joker when viewed from the other. Head-on it kind of looks like Two-Face. "Wow -- solid Batman universe tie-in, GW." Thank you, I had to put my thinking cap on for that one. "Those are panties." Thinking panties. I have a brainstorming bra too.
Hit the jump for a worthwhile video of the transformation in process.
Thanks to Duncan, who made a lenticular that looks the same from both sides. How forward-thinking of you!