Need some advice

Hello. This is your average scrub talking.

I'm not sure how to build against a Kai'sa who builds stormrazor into gunblade into rageblade then straight AP (as a tank). I first tried going jungle item -> tabis when I saw she was building stormrazor, but did a double take when i saw the hextech revolver, which made me want to build adaptive helm, as the enemy team was pretty high on magic damage (neeko + malphite). I then became utterly confused when I saw the rageblade and ludens, and then extremely frustrated when kai'sa would just poke our entire team down (including me) with high damage w's.

It also didn't help that the enemy team started dissing my team for not knowing how to counterbuild (and talked like we left the room, even though I was still there. "They really don't press alt+tab huh", "Garen is crazy stupid" "At least sej built an adaptive" "Nah, she probably would have built it anyway, they're all braindead").

So I'm a little salty and a little frustrated. Any advice? Thanks.