IMPORTANT UPDATE 21/7/17: WITH THE QUESTIONABLE CHANGES TO MULTIPLAYER THAT LAUNCHED WITH THE 6.66 UPDATE 20TH JULY 2017, THE BELOW ONLY WORKS ON THE CONDITION THAT YOU HAD THE SEASON PASS INSTALLED PRIOR TO THE UPDATE AND NEVER DID THE REQUIREMENTS. I
iF YOU HAVE THE DLC FROM A SEASON PASS, BUT NEVER GOT AROUND TO DO THIS FOR WHATEVER REASON, CHOOSE TO KEEP YOUR PROGRESS AND DO NOT WIPE YOUR PROGRESS. QUICKLY DO THIS AND OTHER ARMOUR/TAUNT ACHIEVEMENTS (6 ACHIEVEMENTS IN TOTAL) BEFORE WIPING IN THE PROFILE MENU.
IF YOU ARE NEW TO DOOM, OR RESET YOUR PROGRESS, THEN UNFORTUNATELY THE FIRST TAUNT FOR THIS DLC IS UNLOCKED AT LEVEL 32.
For Owners of the Season Pass Prior to 6.66 Update, 20/7/17 ]
You must own the Unto the Hell DLC to unlock this achievement, however you do not need to do Unto the Hell only DLC maps. It can be done on any map.
An easy 20G, you need to first equip a DLC taunt. Load multiplayer, go to your taunts and if you own the DLC use the RB button to scroll to DLC 1
Select any DLC 1 taunt and associate it to a button on you d pad (I did all 4 so I didn't have to remember which one press.)
Load any multiplayer game, use the directional button you used for a DLC taunt and it should unlock instantly
(P.S. Thanks to No. 1 Richie who pointed out that Private matches does not contribute to achievements.)