That's because he's too lazy to do it. Everyone who has that much knowledge would probably know that a sentence should start with a capital letter and that "I'll" means "I will" and "youre" means "you're". If he doesn't know then he could have spelled "your" instead of "youre". Plus, it's just a tweet you don't need to write the perfect grammar like you should in writing your research papers.
You know, if there is a person who is well known for being a smart ass on the internet, and all of sudden you see a tweet from that person with bad grammar, maybe the first thing to do would be to assume it's bullshit and look it up.
Looks like Mr science man doesn't have very good grammar
and it's kinda cool
not warm
Edit: Or are you resurrecting