I've gotten quite a few of these over the years and learned how to translate them. Please feel free to share any of your own.
"ffs do something useless support" = Body block the hook and die in my place so I don't have to learn how to dodge skill shots.
"ward already" = I was busy slow last hitting minions while they cleared your pink, now go buy another so it can happen again.
"wtf why is bard top" = I just let my lane opponent teleport bot lane for a double kill and expect no consequence.
"don't leave lane ffs" = Babysit me and don't expect me to understand how to play 1v2 for a few seconds while you ward the dragon pit.
"u do nothing" = Vision control mean nothing to my locked camera mode.
"u just watched me dieing" = I just used all my gab closers to engage and didn't think twice about the distance I created between us or the enemies standing in-between.
"why isn't baron warded!!!" = Why didn't you re-ward Baron the second they swept all your existing wards on it so I can attempt to steal it instead of being at the objective in time to contest it.
"report the support" = I just declared myself a jerk and now I will be surprised when everyone reports me instead.