The antonyms for the phrase "be host" include "be guest" or "attend." When one is a host, they are responsible for hosting an event or providing hospitality. Conversely, when one is a guest, they are attending an event and receiving hospitality. In some cases, they may simply attend an event as a participant without being a guest or a host. Other antonyms for "be host" could include words that signify the opposite of hospitality or warm welcome, such as "exclude," "reject," or "shun." Overall, being a host or a guest has implications for social roles, expectations, and etiquette.