When a person has on an item of clothes that is so tight the buttons look as if they were to break loose, they'd fly like a bullet. You know, buttons may-pop off at any time.
Typically used for repeat offenders, it is usually for someone who isnt exactly 'petite' even though they like to dress that way.
"OMG! Did you see Sally's may-pops today. That chick must of borrowed that shirt from her 4 year old." Usually followed by "How did he\she get that on?"