Learn Spanish (Latin America): No se comporten así, es un museo tranquilo. - Do not behave like that, it is a quiet museum.

The verb for "to behave" in Spanish is reflexive: comportarse. The se shows that the action reflects back on the people doing it (literally behaving themselves). Because the command is directed at ustedes (you all), the correct reflexive pronoun to use is se.

Why doesn't the se attach to the end of the verb, like compórtense?

This is a strict rule for negative commands. In negative commands, object and reflexive pronouns must go between the No and the conjugated verb. If this were an affirmative command, the pronoun would indeed attach to the end: ¡Compórtense!. But because it is negative, it becomes No se comporten.

Why is the verb spelled comporten instead of comportan?

To give formal commands to usted or ustedes, Spanish swaps the usual vowel endings. Since comportarse is an -ar verb, its normal present tense ending for ustedes is -an. To make it a command, you swap that for the opposite vowel, making it comporten.

Does así always mean "like that"?