Of course, nothing happened. The pants once worn by Jennifer were now Jon's pants. Since they were his pants now, a wish that he's wearing his pants wouldn't do anything.
After realizing this, Jon decided to change his wish. "I wish that my pants are the same pants I owned an hour ago!"
Which, in a way, did work. Jon felt his clothing transform and he looked down to see he was wearing his normal pants.
Only something was wrong. Wishes, you see, can't be reversed. Jon had wished to get into Jennifer Aniston's pants. If Jon was wearing his normal pants, then the wish would have to come true in another way....
