1. It's a "rule of finger", in fact! :) We use "this" to mean we are indicating the object. Sometimes we are literally pointing at it. "It" doesn't carry this meaning.
2. "Put them hands in the air" - "Them" might be used to mean "those", but this is a very non-standard use. If you use "them" in this way, it will sound as if you are trying to copy (or mock?) a particular group of people. :)
I have no idea where you found the second phrase (the middle part sounds simply wrong, even in a slang context), but "them jeans" means "those jeans", just like in the first phrase.