No offence, but that sounds very casual. Would you avoid proper raiding in WoW if a friend of yours was not good enough to make the cut so you are forced to play 5man dungeons and LFR with them?
Go to: https://us.battle.net/d3/en/blog/731...enet-9-20-2012
Click "Latest" for the comments section and go scrolling through.
Also forum posts requesting the feature on multiple forums below (Some older some newer but it is clear that it has a lot of support):
http://www.diablofans.com/forums/dia...r-offline-mode
https://www.reddit.com/r/wow/comment...option_coming/
http://us.battle.net/en/forum/topic/12404730411
https://www.reddit.com/r/wow/comment...d_this_appear/
http://us.battle.net/forums/en/overw...ic/20744364493
http://us.battle.net/forums/en/overw...ic/20745044649
However if it is a "Group of Friends" wanting to leave X person out because ALL of them find him/her frustrating to play with it becomes very difficult. But X person is a good friend and when you are messing around you are keen to play with them.