Sometimes, I get teammates flaming on my build and questioning my choices.
Anivia: enemy is ad-aa based, I want more mana and cdr, and I already have
Jax: u fcuking idiot
Jax: we lose aldy gg
Graves: why you buy instead of tank items
Graves: you should buy
Rammus: I already have a and a chain vest and I want to be threatening enough for the enemy to not ignore me.
Graves: lol, might as well buy.
Here's a reality check for the next player that questions my build - Screw you people who tell me what to buy (oh hey I swore for once, I must be cool), especially on ranked games. I build whatever items that helps the team and can win the game at the moment. I'm not a bronze player not knowing what to buy. I do not have a set build for every game. I'm not joking around with my item choices, so stop worshipping your Mobafire, Faker or whatever pro-player builds these days.
If by some absurd outlier game that I'm a support Sona with a level 1 Triple Kill (it has happened already), stop telling me that aat level 4 is stupid. I'm still warding actively, I'm still assisting my carry, my role hasn't changed. I'm still doing my job making the enemy lane as miserable as possible. I'm still playing to improve our chances of winning, so shut up.
Oh, on an additional note, unless you're a marksman, get some freaking early defenses appropriate versus the enemy team instead of building glass all the way. I question your thought process of building nil MR vs 4 APs and 1 AD on the enemy team.
Seriously, if I get another Teemo that tells me I'm stupid for building on Waifunivia again...
Edit: I did forget one thing Krufix pointed out rather nicely. Do at least consider build advice of other players, as long as they're reasonable about it and it sounds better than what you currently want to buy.