This jumped into my head and won't get out. Sorry if it reads a little funny, I wrote it sort of present tense and ended up switching to past halfway through and had to fix it. No idea why. But if it's a little difficult that'll be why.
-fs

Bruce sat outside of a café in Paris, the world just getting on with its day, passing him by. He was growing restless, seeing things around him that he should be ignoring. Petty crimes. Things he had told himself he was past stopping. He had chased down a man the week before who had stolen an old lady's handbag. She'd cried, and thanked him in French. The man had spat in his face and turned tail.

Selina had excused herself five or ten minutes before to go to the bathroom. He didn't notice her much while he was people watching anyway. He didn't know how long she'd been gone exactly. He knew he should pay her more attention, but he can't seem to focus any more. Sometimes, he wonders how long it will take her to leave him too. Everyone else has, why shouldn't she be different?

Someone slumped into the seat opposite him, and he glanced up, expecting to see her back, forcing a smile. Instead, he was looking at the unpainted face of an enemy. He recoiled.

"What the hell are you doing here?"

The Joker smirked; no one else was paying them any attention.

He shrugged, still smirking, a mad gleam in his eye.

"I thought you were dead."
"And I thought you were. Seems we're both wrong."
"What are you doing here?"

The Joker licked at the corners of his mouth, and folded his hands on the table in front of him, leaning forwards and baring his teeth.

"I'm where ever you are, Brucie. I go with you. Remember? You complete me."
"That's bullshit and you know it."
"I'm stuck with you. And you're stuck with me. See, I'm kinda, ah, in your head."
"What?"

Bruce looked around frantically while the lunatic opposite him stole some of his drink, hoping to catch someone's eye, but the world was still going about its business, ignoring his plight. His heart sank.

"I've always been in your head. That's the, ah, that's the funniest thing about the whole situation. You have a breakdown, and I, well, I'm created."
"I didn't do all of that. That wasn't me."
"No one can see me."
"What did you do to them?"
"I didn't do anything?"
"What did you do to Selina?"

The Joker laughed, loudly, but no one so much as glanced in their direction.

"Selina? You're still hanging round with her?" he scoffs. "No, no, no. She's been gone ages. You need to find yourself a higher class of criminal. She's probably stealing some old ladies jewellery collection to fund her crack habit. She's no better than that guy who spat in your face last week."

He laughed again at the shocked expression on Bruce's face, which melted into a frown.

"She's not on crack. What have you done to these people?"
"Honey, I haven't done anything. They just can't see me. Only you can see me."

Bruce still glanced around, hoping for any sign that this wasn't in his head. That the Joker wasn't back, here, with him. Terrified that he's actually being haunted by the freak. Doubt begins to creep into his mind about his sanity, but he managed to convince himself that the Joker was the crazy one. Not him.

When he looked back, the Joker wasn't there. He jumped to his feet, and ran to the road, looking for a sign of green hair that he's forgotten wasn't actually green but blond.

Because of this, he missed the relieved expressions on the other diners faces, the men climbing down from the roofs and packing away their weapons. He missed the people raising from their seats and melting off into the crowds.

Selina came round the corner and almost knocked him off his feet.

"Bruce? Are you okay?"

He noticed the dark circles around her eyes, and that she's sniffing, and recoiled away from her too. He forgot that she's been suffering from a cold. Partly because he barely noticed in the first place. She was struggling on without his help, with help from the pharmacy down the road. She kept telling herself he was suffering, probably from PTSD. That he'd wake up eventually and go back to normal. But the haunted look on her face made her heart sink as she wondered what she'd do if he never got better. If he stayed like this forever.

"What is it? You look like you've just seen a ghost?"

His eyes were wide, and he shook his head, grabbed her hand, and forcibly dragged her back to their apartment, locking the door with the key and the deadbolt behind him. He won't tell her what's happened.

The Joker followed them the whole way, hood up, laughing.