It's like clockwork. Around 9 p.m. on any given Friday or Saturday, Scottsdale's vast population (221,000 and change, last we checked) starts swelling by several thousand as the 21-to-35 crowd begins its weekly invasion of the city's downtown entertainment district. Stake out a spot on the outdoor patio at The Firehouse, conveniently located along one of the main drags into the bar-heavy 'hood, and witness this teeming World War Z-style horde of drink-buying, thrill-seeking nightcrawlers marching by the place. It's a nonstop cavalcade of capricious behavior, starring well-coifed club kittens teetering over to Red Revolver in stilettos, inked-up muscleheads ready to rock at Martini Ranch, or the shutter-shade brigade bound to some EDM fest at either Maya or El Hefe. And things get even more entertaining as the evening wears on and the booze wears off, especially inside the chaotic and energetic milieu of The Firehouse. Patrons go wild up until 4 a.m. at the after-hours hotspot, and you're guaranteed to see at least one instance of a sparring dummy being accosted by drunken bros, mock swordplay using baton-like glowsticks, or maybe even the odd food fight. Sure beats gawking at one of those sidewalk fistfights that tend to break out after last call.