Shepard was pissed -to put it mildly- after 'defeating' the Reapers. The Mass Relays were destroyed, somehow Garrus and Tali were able to get to the Normandy and escape onto some random green planet, and here she was, still alive in the rubble.
She slowly got up, coughing along the way, and out of nowhere, the Catalyst-boy appeared, laughing at her. Shepard took out her gun, and shot it, to no effect. Then the boy got taller, and grew around twenty years. The image it took next caught Shepard off-guard.
"Conrad?" she cried out in disbelief.
"Yep." the infamous Conrad Verner, Shepard Stalker, grinned at her. "I finally got my revenge on you!"
Shepard shot the Catalyst again, but the projectile merely passed through his hologram-spirit-thing.
"Ha!" it laughed, "You can't harm me!"
"Conrad, you're an idiot! You know that?" Shepard replied, using her skills to track where Conrad was projecting the image of himself. She found it, and started that way.
The visage of Verner followed, "You won't be able to do anything! I've destroyed EVERYTHING you loved! Just as you wedged me and my wife away with that bullet to my FOOT!"
That made Shepard turn to face him, and point at his face, "You're the one who wanted my autograph! That would've been just fine! But instead you wanted to take my picture, then God-forbid you BEGGED to become a fucking SPECTRE! OF COURSE I SHOT YOU!"
That silenced Verner-Catalyst, and Shepard continued walking, hoping he would disappear. Her hopes came crashing down.
"No matter." Conrad smirked, "You're screwed. The whole galaxy is screwed! All because you signed an autograph..."
That did it. Shepard activated her Omnitool, and accessed communication channels. She had been saving this until the last possible moment, but she wanted to get it overwith now instead of later. "Hey," Shepard spoke into the channel, "Rachni! I have some coordinates for you! He's a big pain in the ass and somehow took over the Reapers with his stupidity!"
They answered quickly, "Very well, Shepard. We will avenge our family."
Conrad realized what she was doing, and tried to stop her, "NO!" trying to grab her arm. He failed, dramatically, as it went right through her.
She smirked at him, "Oh, sorry. You can't harm me."
Off in the distance, the Rachni bombed Conrad's fanclub where he had taken over the Reapers.
"NOOOOOOOO!" Verner screamed as his signal broke down and he was finally dead.
Shepard sighed. Now it was time to find that Prothean and see if he remembered how exactly a Mass Relay worked, and give Joker a piece of her mind regarding cutting tail and running. Then she can continue to make little smurfs with Liara...