if looks could kill

used when someone makes an unfriendly look at someone or frowns at someone  = “se o olhar matasse”

If looks could kill, then the horrible way that the woman looked at me would have killed me immediately.

if so

if that is the case = “se é assim”

The lawyer said that he wants to meet us this afternoon but if so, we will not have the documents ready to discuss.

if the shoe fits, wear it

if something that is said describes you then it probably is meant for you = “se a carapuça serve”

The man was complaining that many workers at his company were lazy. However, his friend looked at him and said that if the shoe fits, wear it.

if worst comes to worst

if the worst possible thing happens = “se o pior acontecer”

If worst comes to worst we can cancel our holiday and go next year.