Say someone phones you and, as often happens, you have no idea who the heck this caller is.
He says, "Hi, this is Peter."
The normal reaction is, "Uh, um, oh, yeah, Peter WHO?"
Instead, try this little trick to save their ego, and hide your memory lapse.
Hi says: "Hi this is Peter."
You say smilingly, "Hi . . . I know TWO Peters. Which one is this?"
When he gives his last name, sound like you are pleased that it is THIS Peter, not that OTHER one."
But, whoops, suppose even his full name doesn't kick start your memory? Then proceed to Step 2. Say, "Hello, Peter, good to hear from you! It's been a long time. Remind me of what we were last talking about." If you really do know the guy, you've saved him the humiliating task of explaining who he is.
But, what if their name is Ichabod, Ellsworth or Esmeralda? (It's not too likely that you know two Ichabods, Ellsworths or Esmeraldas.) In that case, skip step 1, and proceed directly to step 2.
This little trick is not 100% fool-proof. But it's a heckuva lot better than,
"Uh, um, WHO???"