Steps:
- Start an arena game solo
- Type "tf_bot _add 13" into the console (no quotes)
- Make sure you haven't created a navmesh for this map (there isn't one by default)
- Equip the Crit-a-Cola
- Run to enemy spawn, drink the cola as you get to the door
- Peek and shoot the first enemy you see, I used this map because testing showed that bots don't attack past this door, letting me kill the 1st one safely
- Quickly shoot as many bots as you can with the crits
- Cap the point to win the round to restart, you will only get 1-2 kills per round

This may take a few attempts if you mess up but it's the best way to do this solo, it should take under 30 mins.