I can tell you

don't tell me

Used to introduce a guess at a fact or situation, as if forestalling the other speaker's utterance.

I tell a lie

I am mistaken; I thought that what I said (or wrote) was true, but I have just realised that it is not.

I tell you

Synonym of I can tell you.

I'll tell you

Synonym of I can tell you.

kiss and tell

To betray a confidence by disclosing private information, especially of a sexual nature.

let me tell you

Synonym of I can tell you.

live to tell the tale

To survive some difficulty, illness, etc.

only time will tell

Alternative form of time will tell.