Do you recognise the person who shouts hello and knows your name How do you deal with it?

[zeitgeist057]

If it's at all possible, use this trick: introduce them to someone else, but don't give them each other's names. they will have to each say their own name, then is your chance to hear the person's name you forgot. REMEMBER IT!
You can even in a pinch use this with someone you don't know, like introduce the person to your server at the restaurant. It will be weird maybe a little bit, but you can also make it funny.

You can also do more research into how you know them or how they know you, rather. Say something like, "Were you at that party last week at Dave's? I can't remember if I saw you there... " or "Were you part of the group outside the grocery store last week? I can't remember if you were there or..."

Often, people will realize you don't remember exactly when you met and they will give you a break and refresh your memory. Very rarely though, I have had a few where we had some conversation that was epic to them and they will never forget it, but for me it was just another day and I can't recall.