what do i do about twich

Stop him before he gets that insanely fed, would be my suggestion.

2.5 sec

Yeah, that happened.

Don't feel bad. He's a plat and your team was all silver but one gold 5. He also had A LOT of armor pen. Buy pink wards to see him coming for you. 2.5 seconds is a long time to stand there and take hits without reacting. Run or go in on him. Doesn't matter which, at least commit to something instead of taking free damage

If twitch can't land his first spell (e.g. spell block for the poision flash thingy) he wont be able to kill you that easy.

also you could have gone with a teammate for example: you trigger twitch to attack and half way through your hp you use 'Zhonya's Hourglass' (if twitch had activated his ulti at this point you could use 'frozen mallet' (40% slow as melee) and ruined king(25% slow 3sec, long rage) or 'Steraks Gage' (40% of hp added as shield after taking a fixed amount of damage)

Also having a support with 'Locket of the Iron Solari' (shield for 2sec) and 'Talisman of Ascension' (40% movement speed for 3sec)

There are a ton of options, but dont stick with the usual build. If you are dead you can go to your browser to look up which type his skills are (magic/ad) to build a better block.