So, i see a lot of people asking how to do it, and complaining when it doesn't work. This has not been patched, and it wont be for a while because it isn't very common.

1) Have a friend invite you to a PLAYER MATCH.
2) Go to Playercard -> Edit Playercard -> Press B and hover over Save and Exit (DON'T PRESS IT!)
3) Have you friend switch it to a PRVATE MATCH, then change the game mode to Demolition and put it whatever map you want. (Don't only do Nuketown its really obvious lol)
4) Have your friend now switch it to THEATER.
5) Get your friend to Dashboard
6) Wait about 30 seconds and eventually you will be kicked out to a PLAYER MATCH ON YOUR OWN (you should still have your Playercard open on save and exit).
7) Press save and exit on your player card
8) Invite your friend back
9) Wait 10 seconds, then switch it to WAGER MATCH and then straight back to PLAYER MATCH (on your screen it should say your name and one matched player)
10) Then wait about 5 seconds and press B
11) Then don't press anything, and get your friend to invite you.
12) It will then start a 1v1 Demolition game on the map of your choice!

Enjoy! and Merry Christmas!