The ungodly usually laugh at the thought of being judged by God.  It would have happened in Peter's day too.  The apostle now illustrates how God will certainly bring judgement on the wicked, as well as salvation to the people of faith.  2 Peter 2:4-10 is really one long sentence: it is a series of statements starting with 'if' (showing what God has already done) and ending with the conclusion - that God knows how to punish the rebellious and save the repentant (2 Peter 2:9-10). On the way, he uses the examples of the fallen angels (2 Peter 2:4), Noah (2 Peter 2:5) and Lot (2 Peter 2:6-8) who have already observed the judgement of God ... it is no laughing matter.
 
Although we do not know the full story about the rebellion of some of the angels (including Satan), there are helpful clues to the fall of Satan (Ezekiel 28:12-19), and of some angels (Genesis 6:1-4). Peter would have heard Jesus speak of the downfall of Satan (Luke 10:18), and so would John who later wrote Revelation 12:7-9. But whatever interpretation we might place upon those verses, Peter is clear that Satan's kingdom is already under siege by God and the church (Matthew 16:18), and that some of the rebellious angels are already imprisoned one step away from the lake of fire.
 
That would have been encouraging news to persecuted Christians who may have despaired, thinking that justice would never come – in the same way that Israel, as slaves in Egypt may have thought that God had abandoned them ... but God kept His promise to deal with their oppressors and set them free (Genesis 15:12-14). It should encourage us too, especially those who are being battered by godless opposition and unquenched wickedness.  It will not always be that way!  God will deal with your accusers who taunt your faith and mock your Saviour.  After evil has run its course, its perpetrators will be punished (Isaiah 10:12).

So, be strong in the Lord and hold firm to what you believe.  Your enemies are His enemies (John 15:20-21) and the unrepentant will be rewarded for their wickedness when Jesus comes to judge.  Importantly, it is not for us to 'get our own back' because God has said, "It is mine to avenge, I will repay..." (Deuteronomy 32:35).  So, you can safely leave God to be the judge, knowing that He has already limited the power of evil, and will complete its purge when Jesus comes again.