Personally, it has nothing to do with me "being better", but with them being illogical. A few examples:
- The most common one - If you have died 3 times from an enemy player, why do you keep running into them, why are you not staying under your own turret and waiting out the laning phase? You are consciously feeding, making the whole team lose, and you expect people to be fine with that? This is the player that is so convinced they are the best, they can't accept the fact that they can't kill somebody so they keep trying and failing.
- I played with an adc who kept getting hit by every single Zilean bomb, like seriously,every single one. Not even trying to avoid them. There was no way to support such a player and ofc, it lead to another loss.
- Junglers who keep farming monsters for way too long when the rest of the team is getting ganked. Not always flame-worthy but certainly annoying.
- Players who consciously pick a champ that doesn't work in their lane. Now, this is subjective cause almost everything can work if you're good at it, but playing support with a champion that literally has no way to support is again consciously making your team lose.
- Players who auto-lock and threaten to feed if you don't let them have it their way.
- Plus, all of the above-mentioned examples can be fixed/made less serious if the "noob" in question would communicate with their teammates, but in most cases, they either refuse to listen or don't even understand English.
Also, if griefing and feeding are reportable acts, then consciously making your team lose by playing a role you don't know how to play should be as well. There are ways to learn without making your whole team lose.
In short, I would personally never threaten somebody's life or insult somebody's family because that's just childish nonsense. However, if I, you, or anybody else, see somebody purposely being illogical, playing in a way that is definitely leading to a loss, and are the only reason for that loss, then I think it's completely justified to call that person an idiot or tell them they suck. Why? because not saying anything means you're accepting the situation, you're allowing the bad player to bully you by not reacting since again, you can't report them for being bad. And if those simple words offend them so much, then quite honestly, they shouldn't be on the Internet.