• Open the Playground
  
• Click the "List" icon
  
• Click "Fight!"
  
• Click "make them battle"
  
• Select Rohit, then Jonathan. And keep doing this until the achievement unlocks

At some point the infotext will read "Rohit uses his IMPOSSIBLY BLUE PANTS to stun Jonathan's optic nerves" (otherwise it will say "Jonathan uses his UNWAVERING CHOICE OF FONT to annoy Rohit until he explodes!")

Congratulations!