El Mexi-Rock Cafe, 28411 Marguerite Parkway, Mission Viejo. Open Monday through Saturday 3 p.m. to 2 a.m. (714) 364-6674. By day it’s just another pastel-colored Mexican restaurant. But after 9 p.m., the rather small dance floor is generally packed with a youthful mix ranging from long-haired rockers to close-shaved hip-hoppers. The sound system is good, meaning that the only place for intimate conversation is out in the parking lot.