However, I will smile and laugh with you and pretend like I do until I remember or someone else comes by and helps me out.
Nothing against you in particular, it just happens sometimes.
Yes, we met before. We probably chatted and we may have exchanged business cards and a joke or two, however, I don't remember your name, or anything about you to be honest.
And I'm just me. I don't meet that many people. But imagine a creative director or a recruiter. Imagine how many emails they must get in a day. How many business cards they hand out. How many short conversations they have between here and there. It adds up and it's hard to keep track of every face, name and story.
This is why you have to stand out (I wrote about this here) and you cannot be afraid to remind people who you are.
In emails: Refresh their memory on when and where you met, maybe even give a reference to what you talked about to recreate the context and then state your business.
You don't have to attach photos or anything, just keep it simple: "Hey, I'm Julie, we met at the Nerdfest last Tuesday, I was wearing hot pink glasses."
In person: Don't be afraid to reintroduce yourself. Having a convo with someone who doesn't remember you is a waste of your time. Going through who you are a second time will help reenforce the information and hopefully they'll remember this time.
Don't act annoyed that they don't remember or try to hard to job their memory. Just start anew and try to do a better job of standing out.
On LinkedIn: Always include a note with your invitation to connect. Say who you are and where you know them from.
I HATE getting messages that someone indicated that we're colleagues or friends when I have no idea who they are. (Lies! All lies!) I used to decline automatically (stranger danger) but I've started writing back and asking who they are, hoping it'd prompt people to realise we're not on Twitter, this is the grown up league.
Don't take the forgetfulness personally. And maybe it'll work to your advantage - consider it a second chance to leave a great impression.