The past subjunctive is used with as if / as though. It indicates the unreality, impossibility or doubt that happens in the present form.
Sub + present tense + as if / as though + past tense.
He talks as if he were a king.
The student talks as if he knew everything.
The boy behaves with me as though he knew me.
He talks as if he knew nothing about it.
The verb used prior to the subjunctive can be past form also without changing the tense of subjunctive.
The man talks / talked as if he were the boss of the office.
She looked / looks as though she were an innocent girl.
She behaved with me as if she did not know me.
The police-man behaves with the man as if he were all in all in the office.
She looks / looked at me as if she had never seen me.