I had a yi who built 3 tears, than after about 5 minutes sold everything and bought the items for a zhonyas. He was just hovering around the enemies dancing, and at the end of the game when our team said to report him, he responded with "I was trying a new build". Does this count as trolling?
This was also a ranked game.
It does count as trolling. You can report them after the game and Riot will review it.
Definitely trolling. He didn't even dealt damage at all in that game.
Sure he can.
Riot says that you are basically allowed to go 
jungle and call it "trying out a new strat".
The only thing that Riot nowadays considers bannable trolling is actively running it down and obviously trolling. Basically everything else is fine as long as you have some shitty excuse for it.
I mean, two tears could be understandable to get archangels and manamune since Yi does have ad and ap scaling... I don't think it's a good item build but it could be potentially useful? Three or more is intentionally trolling IMO. I'd report it unless they were all purchased at like the end of the game right before the nexus exploded.
It's either trolling, or having a genuine problem with understanding game mechanics.
To answer your question, yes, he can call it whatever he wants. You can report him if you want but you'd be better off just laughing it off and few people like a tattle-tale anyways. If someone trolls often or doesn't try very hard to win, they'll end up with very low mmr and will be matched with other players who play on their level anyways.
Yes he may.
I've seen a Swain build nothing but 
I mean, it's not a build i ever heared off xd
But seriously just report and let the admin/bot system deal with him.
It does not matter what he said, intent and results are what matters. He trolled, thus he trolled.
Three actually works I think: Archangels, manamune, one unupgraded tear for mana.
How does it LOWER your stats? It's not efficient but it shouldn't lower your stats.
