Learn Spanish (Spain): ¿Por qué ustedes se ponen histéricos a veces?

The verb ponerse is a verb of change. While están histéricos simply means "you are hysterical" (describing a current state), se ponen histéricos means "you get hysterical" or "you become hysterical". It highlights a sudden, temporary emotional reaction, which is exactly how this verb is used.

When should I use ustedes in Spain?

In Spain, ustedes is the formal plural form of "you". You use it to address a group of people respectfully, such as older adults, clients, or strangers. If you were asking this question to a group of friends, you would use the informal vosotros and say ¿Por qué vosotros os ponéis histéricos a veces?.

Why is the adjective histéricos in the plural form?

When using ponerse with an adjective, that adjective must agree in gender and number with the subject. Because ustedes refers to a plural group (masculine or a mix of men and women), the adjective takes the plural masculine form histéricos. If the group were entirely female, you would use histéricas.

What happens if I forget the se and just say ustedes ponen?

You would completely change the meaning! Without the reflexive pronoun, the verb is just poner, which means "to put" or "to place". To mean "to get" or "to become" (expressing a physical or emotional change), you must use the reflexive verb ponerse.