GEN Completely disregarding how things ACTUALLY happened after the Insiders arc, Bart plots.
Bart, current alias Kid Flash and therefore the fastest teenager in the world (unless you want to get into some of the technicalities of time travel, in which case he's the fastest twinkle in the eye of the twinkle in the eye of a superhero who's now dead), proved that he still hadn't mastered jumping fast enough that people operating at normal speed didn't notice when one of the Batclan startled him. Whether Tim occasionally used this knowledge for his own amusement, however, is completely irrelevant to the story. (He did. You should see how high speedsters can jump.)
In not even the blink of an eye, Bart had gone to get a notebook. "I have a very important mission," he wrote (having apparently learned quite a bit of Japanese when he read the entire San Francisco library). "Do you have any capes I can cut up?"
Tim opened his mouth to answer, but found a hand in the way. Bart waved the notebook between them. Tim cocked an eyebrow, but took it and the pen and wrote (also in Japanese, just for the hell of it) "I guess I can always say you didn't ask first. Why do you need one, anyway?"
"I've got an idea to pay Conner back for letting himself get brainwashed, but I need maximum ninja stealth to pull it off."
"Revenge? Are you serious?"
"Yup. I've already got all the make-up together, too."
Tim cocked an eyebrow. "This I've gotta see."
Grinning, Bart wrote a final message before vanishing to take one of Tim's spare capes. "Awesome. Ask Raven if she can keep someone asleep for a while, will you?"
Much later, long after everyone else had gone to bed, Tim and Raven went to Bart's room for the top secret mission. He'd turned Tim's cape and boots into a passable ninja costume, complete with a make-up-holding utility belt. He inspected them both quickly, nodded, and indicated that they come with him. Quiet as owls they snuck to Conner's room, vibrating in through the wall to minimize the risk of waking him before Raven could convince him to keep sleeping.
Fortunately, everyone's favorite Kryptonian clone was sleeping on his back. Bart signaled Tim, who pulled out a small flashlight and aimed it at Conner's forehead. Then Bart pulled out a razor and carefully, oh so carefully, shaved Conner's right eyebrow off.
"But Kory, it's Gar's turn to wear the mumu, I wanna be the walrus," Conner muttered, swinging one open hand in the general vicinity of Bart's skull. Bart dodged it, and the three conscious Titans froze as they waited to see what would happen. Conner mumbled something incoherent and turned over onto his side, leaving the right side of his face in a perfect position.
Tim watched, silently amused, as Bart moved to the head of Conner's bed and began to carefully apply the make-up around the freshly debrowed eye. When he'd finished, they snuck out as quickly as possible and returned to their respective rooms.
"What the hell happened to MY FACE?!" Conner's voice echoed through the tower the next morning. Raven disavowed knowledge, Tim practiced his Batmode, and Bart caught a glance before running for his life. The rainbowy flower he'd painted around Conner's eye had come out perfectly, if he did say so himself.
Even if he had to live in eternal fear of supernoogies forever after.