It's like " I dont care" in a rough form. Not, not really cultural)

мне наплевать=I don't care

Although one might use "Мне наплевать" as "I do not care," typically it has a stronger connotation that might be compared to "To hell with it" or similar.

Мне наплевать - means "I don't care". Literally, we can translate that in English as "I spit on it". Usually, people use this expression when they very angry about something or somebody. Often, this expression use when people swear with each other. This expression is rude and can seriously offend person but this is not filthy language.