I have the best solution for 4v5s
If you are on the side with the afk player you need to blame the other three players on your team for the loss. Don't blame the player that ISN'T there. No no no no. Blame the top that got camped by the enemy jungle that free farmed your jungle because your's was dc'ed. Noob clearly fed because he is garbage. Blame the support that had no adc to lane with. That dumbass just has no idea how to ward, play safe and farm under tower. Even if the support gets dove by 3 it is his fault for not warding top lane. Make sure to blame your jungle for not ganking. That dumbass just sat mid all game trying to deny that free farming Katarina. If he was any good he would shut her down AND farm jungle AND gank lanes. Fucking scrub. If you get ganked because the enemy roamed from the afk lane remind your team how trash they are for not keeping pressure so the enemy stayed in lane.
If you are on the side with all five players you need to make sure to talk about how great you are in all chat. Remind the enemy that if they were as good as you they would win this 4v5 no problem. A dc is just an excuse to be a noob. Remember to also take your time taking objectives. REALLY farm those kills. If the enemy gives up be sure to call them trash and refuse to push a lane. Focus on padding your cs numbers and dragging the match out as long as possible. If they aren't miserable then you aren't doing it right. They need to feel bad for being so bad. If the enemy asks you to report the afk player you have to stand up for the afk player by calling their teammates whiny noobs. I mean, what kind of assholes ask for reports behind someone's back? Those cowards don't even have the balls to ask for reports to the player's face.
Follow these guidelines and you will be a shining example of why 4v5s aren't just about the afk player.