Do you guys know how to do this to your jeans?

Use a boxcutter to cut parallel lines close to each other, in a vague diamond shape on each knee and strips below. Don't cut completely through the fabric, just enough to reveal the threading. Then either crawl on concrete (may be painful), or use a giant nail filer and file away at the jean fabric until it's frayed and looks like that. Feel free to use the boxcutter more if you like.