Friendly + bad vs Toxic + good
The bad but friendly guy who makes the game impossible to win regardless of your performance effectively wasting 20 minutes of your time + the time it takes for you to get back those LP and the probability of him being a troll who doesnt surrender despite the game being lost 100% ( dont you love those) or The toxic(not including hate speech etc) but good player you could always mute who is likely to carry you and give you free LP in an environment where winning should be most important(ranked)