It’s perfectly okay to say this if you’re contrasting two pairs of pants.
“I didn’t find your OWN trousers, but I found the pair you borrowed.”
“You didn’t go to the party with your own girlfriend.” (In other words, he took someone else’s, or else it’s shocking somehow that he didn’t take the girl even though she is his girlfriend.)
For foreigners, the hazard of the word own usually comes when they try to use it without a possessive adjective. You’ll hear them say things like, “Do you have an own car?” which is totally wrong. It should be “Do you have your own car?”