This applies to all non-sup laners too.
Last year when i first started playing league me and my sis were duoing coop vs ai, i was the supp (
)she was the adc(
). I was still new to support at the time and our team started falling behind a bit, so i was in the middle of building:

So that we could clear minion mobs faster together and it was very effective, we managed to quickly push to the enemy base fast but our top was struggling and mid was doing fine. he had the most kills pretty fed and obviously did not need help. but anyway our mid laner goes:
: Sona what are you building?
: Attack speed/CDR/AP
: Duh..No s*** i see that, but why?
: So i can help clear the waves faster since we are falling behind. I also need the CDR and mana to better support and keep you guys healed and buffed.
: But your a support, you don't need thoes.
: Oh? what should i get then?
: Nothing. Don't buy gear/items ever on support...
: Why? doesn't these help me to better support you guys?
: No your a support all you need is your kit. don't buy items
: But i run out of mana too fast, and the CDR helps me keep spells on you guys so you can live longer..
: No the only thing your going to do is go 0/3 and feed. You are a BAD support.
: Your saying because i bought items that do nothing but give benefits somehow i'm going to die more often because of it?
:Roaming to top to help out
: Yes. Stop being bad pls. And stop roaming always stay by your adc don't feed pls.
: our top laner, silently struggling and is pushed all the way to our base..
: Stop, you just died 4 times over nothing! stop typing and start playing!,mind your own lane if your not going to be helpful omfg!!.
: But i looked up a lot of guides before picking up Sona to help me play more effectively.
: OMG are you trolling or something?.
And i died because this supp is being soo bad.
: Then stop typing.
: Dude stfu and just play, she's doing FINE.
: These guys are trolling this team is soo bad, Sona after this game don't ever play supp pls your bad.
: Still new to League ,Can't find the mute button
We still won. making sure my adc did not die, my mana pool NEVER ran dry and i was able to spam skills for days without dying for the rest of the game.
This guy was acting like a **** and he wasn't even my adc and didn't even roam to help out other lanes himself so our top ended up feeding after one guy went afk. wtf supports can't even help other lanes? stuck with my adc till death do us part???. -_-