1. Take them star gazing!
Then, while they're looking through the telescope, tell them you wish they were as far away from you as those stars.
2. Stop feeding them!
It's easy to love someone who gives you food. For example, cats! Stop giving them food and they'll fall out of love with you.
3. Flash the lights on and off!
Like bars do to let customers know it's closing time! "You don't have to go home but you can't stay here." It's subtle but your other half will get the message eventually.
4. Show them the door!
It's a pretty straightforward tactic. Get out.
5. Tell them that they're not your soulmate!
Even if you don't really believe in soulmates! It's still a legitimate excuse to break up.
6. Leave them a series of clues!
The clues will eventually lead to a note telling them your relationship is over! And by that point in the scavenger hunt they'll be far far away from you.
7. Tell them they haven't been on your mind!
This will be more believable if you've also forgotten their name.
8. Reject their proposal!
It's quite harsh, but necessary.
9. Pretend to get amnesia!
It happens in movies all the time! Your relationship never happened so no feelings are hurt.
10. Make up a story that involves you going on the run!
From the police, from the mafia, whatever it takes.
11. Walk away dramatically into the mist!
You may need to check the weather constantly until conditions are perfect.