I dont really know when to buy it. Is there like a "rule" on how tanky the team should be and what champion ur playing against. Cus now im playing cait and are against nautilus, cho gath and volibear. Should I buy bork?
yes you should
Buy it if you are 
Generally adcs dont buy botrk, except Vayne and Kindred (because of their W). Mostly assassins and/or fighters that benefit from attack speed get it.
champs that have atk-speed abusing mechanics can benefit greatly from bork, as well as other on-hit relevant items. atm vayne, kog, and xin, and ww are probably the most commonly seen.
I personally like it on varus though as a super off-meta build against tanks.
attack speed champs or mobile champs can use the passive and active very well
if anyone on the enemy team has an item that gives more than 200 hp.
Kalista !! Why is everyone forgetting about her?
