First comes simple posturing. A little extra makeup, a few buttons undone, maybe a little more leg. After that things can escalate pretty quickly, especially if there's a changing room around. Or just clothes in general. Strutting, flirting, and eventually trying to get the other so flustered that they back off.
Granted, some instances aren't as fast, and can take course over several days. Although that usually is more related to steady oneupsmanship rather than outdoing one another