* A battlefield: Emphasizes the competition for tables, food, and social standing.
* A zoo: Highlights the chaos, noise, and diverse (sometimes clashing) personalities.
* A pressure cooker: Focuses on the intense social pressures and anxieties.
* A tribal gathering: Emphasizes the formation of social groups and cliques.
* A survival of the fittest: A more dramatic metaphor emphasizing competition for resources and social dominance.
* A poorly managed buffet: Focuses on the chaotic and sometimes unsavory aspects of the food and the environment.
The best metaphor will depend on the specific aspect of lunchtime you want to emphasize.