Although swagger has been nerfed in this generation through accuracy and confusion hit chance reductions, it is still problematic for 2 reasons.

The first is the presence of tapu fini’s ability to activate misty terrain making self swagger strategies prominent. With this, tapu fini can boost physical attackers damage output past their usual checks such as intimidate cycling and strong resists while also protecting them from status. This problem is exemplified in Snorlax and its curse set. In usual instances the curse set is easier to set up but gives up the power and immediate sweeping potential that the belly drum set has. However with swagger support, Snorlax receives both the immediate power and bulk to break through checks such as Ferrothorn, Landorus-t and Amoonguss.This has made Doubles OU into a set up heavy metagame where a combination of Snorlax/Zygarde/Physical attacker and Tapu Fini can bring a game back for the user if the opponent has been caught in a bad position. This is similar to the effect the combination of Azumarill and Jirachi had last generation where the threat of set-up made positioning have an overbearing impact on games. Though swagger is not the only culprit of this set up heavy metagame its ability to boost pokemon like Snorlax past their checks pushes it over the edge.

Another problem with swagger is its interaction with Marshadow. With the combination of Spectral Thief and a swagger pokemon faster than Marshadow, Marshadow will often receive both a ko and a plus 2 attack boost. This creates a lot of 50 50 scenarios where the Marshadow player will gain a significant advantage if guessed correctly due to the plus 2 attack boost. These 50 50s are undesirable as they promote coin flips over skill and ability to maneuver board positioning.

With these two reasons I am voting to ban swagger.