"Jeans are" because you don't have a jean, you have jeans. They are plural therefore ARE is used as opposed to Is for a single object.
AKA the mouse is in the corner, versus the mice are in the corner
When people say jeans, they are referring to TWO jean-pantlegs, but you don't only wear one jean pantleg do you? So, the way to refer to jeans is always plural, just like how you say "I bought a pair of pants" rather that "pant."
it would be are b/c jeans has the s on the end just like in spanish its used as plural too.
i think jeans 'are' is correct...but yeah i never thought about it...weird eh