Toxic players, 1v1s, and Arams

Why do players in ARAMs have to be total jerks to people. For instance, I just got out of an ARAM with a less than desirable team (they weren't that good overall) but nobody was being toxic. When all of a sudden a player on the other team by the name of Techonic (playing Leona) starts trash talking our already behind Xerath about how he can 1v1 him, despite it being the REST of this guys team that was doing much of anything. I honestly don't know if this guy is trolling or just dumb because he didn't seem to understand that fact that when you jump on top of a Xerath, he's gonna die. Doesn't matter who you are. Post game proceeds and this kid just keeps trash talking, while I'm trying to vouch for my Xerath. This kid eventually ends up saying "you want to 1v1 me bro?" to which I reply "yeah sure." He proceeds to tell me to add him, which I do immediately, at which time he leaves and I don't hear from him again. Why do these kinds of people exist? Throw into the mix that this kid is trash talking an unranked guy who I'm guessing is newly level 30, and he knows it. And more importantly, since I didn't get to report him properly, consider this my report to Riot. These kinds of players make this community look horrible and on top of that its not even in a game mode that's worth getting competitive over. Rito pls.