College student alcohol consumption is a major concern, and is known to increase during the celebration of special events. This study examined a student-constructed holiday, State Patty's Day, at a university with a dominant drinking culture using three sources of data--coded data from Facebook groups, daily web surveys from first-year students (N = 227, 51% male, age 18 to 20; 27.3% Hispanic/Latino; of non-Hispanic/Latino, 26.9% of sample European American/White, 19.4% Asian American/Hawaiian/Pacific Islander, 15.9% African American/Black, 10.6% more than one race), and criminal offense data from police records. Results indicated that messages about State Patty's Day on Facebook focused on drinking and social aspects of the holiday, such as the social context of drinking, a sense of belonging to a larger community, and the social norms of drinking. These messages were rarely about consequences and rarely negative. On State Patty's Day, 51% of students consumed alcohol, compared to 29% across other sampled weekend days. Students consumed more drinks (M = 8.2 [SD = 5.3] drinks per State Patty's Day drinker) and were more likely to engage in heavy drinking on State Patty's Day, after controlling for gender, drinking motives, and weekend, demonstrating the event-specific spike in heavy drinking associated with this holiday. The impact of this student-constructed holiday went beyond individual drinking behavior; alcohol-specific and other crime also peaked on State Patty's Day and the day after. Event-specific prevention strategies may be particularly important in addressing these spontaneous, quickly-constructed, and dynamic events. (Contains 2 tables and 1 figure.)