The Local Way to Say It
¡Ojo! When something feels a bit off, a little suspicious, or you're just plain annoyed by a situation, Madrileños don't say they'reThe 'Grammar Math'
The 'Grammar Math' for estar mosca is surprisingly simple, yet powerfully idiomatic. It's not about ser, the verb for inherent qualities, but estar, which describes states or conditions.Estar + Mosca = To be suspicious/annoyed (temporary state)
Here, mosca functions as an adjective in an idiomatic expression. It describes your current feeling or state regarding a situation.
Think of it like this:
Yo estoy mosca (I am suspicious/annoyed)
Tú estás mosca (You are suspicious/annoyed)
Él/Ella/Usted está mosca (He/She/You are suspicious/annoyed)
Nosotros/as estamos mosca (We are suspicious/annoyed)
Vosotros/as estáis mosca (You all are suspicious/annoyed)
Ellos/Ellas/Ustedes están mosca (They/You all are suspicious/annoyed)
It's always mosca, regardless of gender or number, because it's a fixed idiom.