In Chapter 2 the author shares a long rebuke of false teachers, and in the midst of this tirade and warning we get to these enigmatic lines:
Bold, arrogant people! They are not afraid to slander the glorious ones. (2 Peter 2.10b)
This isn't the only place in the New Testament where we read about people slandering "the glorious ones." We find it also in the book of Jude:
In the same way these people—relying on their dreams—defile their flesh, reject authority, and slander glorious ones.
So, who are these "glorious ones"?
Most scholars agree that "the glorious ones" refers to angels, and that the "glorious ones" can also be translated as "the Glories."
For context, it should be noted that in 2 Peter and Jude some of the weirder cosmology and angelology of the Bible is on display, especially influences from the intertestamental books of 1 Enoch, 2 Enoch, and Jubilees. For example, in 2 Enoch 22.7 Michael the archangel along with the glorious ones, the angelic court filling heaven, are mentioned. Michael is also mentioned in the passage from Jude, so a connection between 2 Enoch and Jude is possible. Relatedly, some scholars think 2 Peter has Jude in mind, which would link all three texts that mention "the glorious ones" of the angelic court.
We might imagine here the heavenly throne room scenes from Revelation. For example, in Revelation 4 and 5 we read of the four living creatures who sit around the throne of God giving glory and honor unceasingly singing, “Holy, holy, holy, the Lord God the Almighty, who was and is and is to come.” Perhaps the four living creatures are among the glorious ones? Along with the four living creatures are "myriads of myriads and thousands of thousands" of angels who also sing, “Worthy is the Lamb that was slaughtered to receive power and wealth and wisdom and might and honor and glory and blessing!” Perhaps this multitude of angels in the throne room of God are also the glorious ones?
It's unclear exactly who the Glories are. But we can surmise that the false teachers in view in 2 Peter and Jude are, in some way, disparaging the Lord's heavenly courts and/or angelic servants. Cursing heaven, as it were. Failing to give due honor to God's angelic servants and stewards.
This is, admittedly, pretty strange stuff. But regular readers know I like to ponder the cosmological oddity of the Bible as a jolt to my settled modern assumptions. The world is so much stranger than we can imagine.
Keep Christianity weird.