It's amazing how many people are doing this, particularly YouTubers. Reverse Boosting is when you have a side account with tanked stats (below 0.50 k/d) in which you join session with your main on a formed lobby and then back-out with your side account. You are basically in a exceptionally weak lobby with your main account being the end result.
It's so blatant and the quality of the content produced is absolutely embarrassing - even recruit bot matches are more of a challenge and livelier. Here is the most infamous example which is absolutely cringeworthy to watch especially when the dude tries to be overly dramatic:-
COD YouTuber ExclusiveAce put out a funny video after trying this tactic and this was the end result:-
This is borderline cheating really. These players are incredibly bad at the game and this could be down to age, general ability or even a disability and the last thing they need is some sweaty cancer content creator to obliterate the lobby and shame them in the process. Considering how strict SBMM is in COD now, it's farcical that such a simple and effective loophole exists. Activision however get paid off twice for this to happen so I wouldn't expect it to be plugged at all.
If you're ever watching a video and you see a 3 k/d player posting a score of 100-0 you know exactly what they've done to get it.