Used as a verb by some gay men to describe the attitude and actions necessary to make something fierce. Often used when an outfit or object or action is way over the top and cannot be handled with any meekness.
Girl, you will have to seriously fierce that outfit to make it work but you know you can.
Look! She is fiercing those shoes.
I hate this party and these people so I am going to fierce my way to the front door and then leave.