I know this feeling. It's tough because when they're your friend, you want to still spend time with them and maybe help them, but you also want to win haha.
There's a couple I play with (husband and wife) who just aren't the best at the game. They're fun to talk to, but they can get tilted pretty quickly, and don't understand a lot of the basics when it comes to the game (like positioning, when to get objectives, roaming, matchups, etc).
The husband is the worst when it comes to getting tilted. He played GP top once and was getting trashed by the enemy top laner. I tried helping him but he was already tilted at that point to where he quit the game and locked himself in the bathroom haha... They both also get angry at people who play "off-meta" champions and complain even more when they get beat by them with phrases like; "Oh guess this person can't play a real champion to go against me." or "wah look at me I can't play real champions in lane wah!" (whatever the hell that means...) Even got angry at me for playing off-meta too o_o; (Blitzcrank jungle is quite a lot of fun! Or building tanky ADC champs haha :) )
I do try to help them and give them advice when I can, but it's tough when they don't want to listen or even acknowledge it. Especially when you try to help them with their "mains". That's like walking into a mine field wearing a dynamite suit x_x
All I can say is to just play games on your own every now and then. Play with them just to enjoy their company, but don't forget to have "you" time and play by yourself or with other higher skilled friends :) Really does help even out the losses and frustrating aspects of playing with lower skilled friends.
