Giving sealed commercially produced snacks/candy to the crew isn't weird, it's being nice. Don't do it with expectations of an upgrade or anything though.
I've never once gotten a bad reaction. A family member who works at an airline got me started on doing it.
A commercially sealed snack can still be tampered with. My QF captain friend said he does not have the authority to upgrade so giving a few candies to a FA probably won't garner an upgrade either.
If they are not impressed do you think the FA's will say so. They'll just express their delight then throw it away when you are not watching.