Triforce on Vi?
Just played Vi for the first time in ranked after doing well with her in normals. Had a really off match, going 5/11/9. But I started off well, going 3/1/2, so I went for Triforce. My whole team questioned me on it, and when I pointed out it was even an "essential item" for her, they just gave me a "lolnoob" response. So, just to prove a point, I hopped on Lolking and scanned all the top guides (including one from a diamond player) for her. The closest any of them got to steering you away from Triforce was one that said to buy it when you're ahead, which I was at the time.
I then asked my friend who, despite having a reputation for doing stupid things in League, plays a lot of Vi. He told me it's bad and not to build it on her. At all. Never ever. Is it actually a "bad" item on her or did my teammates and friend just have no clue what they're talking about?

Instant camp clear with E later and keeps her hp topped up
active after using her ulti to keep the enemy team in place, and the best armor/hp item in game
makes sure I have the opportunity to use my ult, denies a spell that could throw me off and is the best mr/hp item imo
or
or
depending on the teams need - Hexdrinker if huge single target burst exists from an AP champ and I am ahead, Frozen heart if enemy team is mostly AD or they have multiple auto attack threats, Solari if they have aoe magic damage or someone else on my team is ahead and might get focused by AP burst.
usually for quicker early ganks and might swap out later once teams start to group)