Are the expressions "out of the blue" and "out of/from thin air" similar?
Yes, they are. Both expressions mean "do nada".
What is the corresponding expression for "fiquei sabendo?"
I've heard...
Put the expression "just in case" in a sentence.
Ex.: I'll bring an umbrella, just in case.
What is the meaning of "water off a duck's back"?
Letting it go or having no effect.
What is the corresponding expression for "colocar panos quentes"?
Pour oil on troubled waters.
What is the meaning of "sitting on the fence"?
Hesitant, avoiding to make a decision or taking sides.
In English we don't say "taste of your own poison" we say...
Taste of your own medicine.
Is there an acronym for the expression "by the way"?
Yes, there is. It's BTW.
When we use ASAP, what does it mean?
As soon as possible.
What is the corresponding expression for "nos dias de hoje"?
In this day and age...
When we use AFAIK, what do we mean?
As far as I know...
This one is very similar in Portuguese "rub ____ in the _____".
Rub SALT in the WOUND.