Okay, it happens.  You run into an acquaintance you've met, and gulp, maybe even several times.  Yet, you can't remember their name.

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Well, there are some tips on how to handle this gracefully.  According to Life Hacker's Magazine.

In some instances, honesty is probably the easiest answer. Telling someone you’re bad with names and asking them point-blank isn’t a terrible idea if you’ve only met once or twice before; a simple “I’m sorry, I’m not great with names. What’s yours?” will suffice.

When not to admit,

In other instances, like a job interview or you’ve met them several times, had lunch, and even celebrated birthdays together, it probably wouldn’t look good to ask them for their name at this point.

Other tips, from a recent Reddit thread,

Hand them your phone and ask for their contact information—hopefully, they’ll fill in their full name. I would preface this request by proposing getting together for coffee or lunch, just to make the question feel less random. If this is in a job interview or other professional setting, ask for their email address instead which should hopefully contain at least part of their name (or ask for a business card).

Lastly, if these tricks fail try introducing yourself.  I do this one all the time!  Hi, I am Juli, not sure you'd remember me.  Then folks usually get the hint, but NOT always.  Then maybe the connection wasn't meant to be.