* A slang term: Without more context, it's hard to say exactly what it means. It could be a slang expression for oral sex, depending on the situation and the people using it.
* A regional expression: There might be a specific meaning in a particular region or social group, but without more context, it's difficult to know.
* A misheard phrase: It's possible you heard a different phrase altogether and misheard it as "tongue it".
To get a better understanding of what "tongue it" means, you need to provide more context:
* Where did you hear it?
* Who said it?
* What was the situation?
With more information, it may be possible to understand what the speaker meant.