Someone please help

I need potty training tips extremely bad. My son is 2 and a half and absolutely refuses to use a potty. And I mean he will flip out if you even mention it. If you say "big boys use the potty!" It's no I'm not a big boy I don't wanna be a big boy. I've tried putting him in underwear and sweatpants so he got that wet uncomfortable feeling. I've tried rewards such as a sticker chart. I've tried underwear under the diaper. I've tried running around naked and he just pees on the floor and laughs. When he poops he says "haha mommy I poop now change me" I am at a complete loss of what to do and will accept ANY tips.