estar com um pé atrás

You use it just like the verb 'to be'. You can say eu estou (I am) or ele está (he is). It works perfectly when someone makes a promise that sounds too good. If a friend tells you they found a way to get free flights, you'd say estou com um pé atrás. It is very common in the present tense. You can also use it in the past, like fiquei com um pé atrás. This means you became suspicious after something specific happened.

Use it when a salesman is being a bit too pushy. Use it when a stranger asks for a weird favor on the street. It is great for business meetings when a deal seems risky. You can even use it in dating! If someone is 'too perfect' on the first date, tell your best friend you have um pé atrás. It shows you are smart and not easily fooled. It is a very natural way to express doubt.

Don't use it for simple physical fear, like being afraid of heights. It is about suspicion, not phobias. Avoid using it in extremely formal legal documents. While it is common in offices, it is still an idiom. Don't use it if you are 100% sure someone is lying. If you have proof, you aren't 'suspicious' anymore; you are certain. In that case, use stronger words like mentira (lie).

Brazilians are generally very warm and welcoming people. However, there is a cultural concept of the malandro (the trickster). Because of this, people have developed a healthy sense of caution. This phrase captures that 'street smart' attitude perfectly. It dates back decades and is used by everyone from grandmothers to teenagers. It reflects a survival instinct to avoid being taken advantage of in daily life.

You might hear people say ficar com os dois pés atrás. This is the 'level 2' version. It means you are extremely suspicious, like you are ready to jump backward! Another variation is pôr o pé atrás. This implies the moment you decided to start being cautious. Both are very common in spoken Portuguese across Brazil and Portugal.