When you can't remember the name of someone, you can call him or her "What's-his-name" or "What's-her-name":

It stars What's-his-name. You know, the guy from Titanic.

A: Where is it?

B: I gave it to What's-her-name.

A: Isabelle?

B: Yeah, I think so.

In sentences like these, "What's-his-name" replaces the person's name.

This phrase can seem rude because it seems like you don't care much about what the person's name is. Or it can just seem like you're forgetful and relaxed.