How do you ask a guy out that likes another girl?

FLIRT WITH HIM!!!!! And if flirts back SWEETIE GO 4 IT!!! No. That would make you seem like a slut. I've met a lot of those girls. Relationships and crushes don't last forever. Have patience. While waiting, build a relationship with him. Start out as friends and work your way up until your close enough to flirt. Be sure you get the timing perfect or else you'll get stuck in the friend zone. I got stuck there with someone, and it's difficult to get out.