First of all, we have all felt foolish at one time or another. It's best to just laugh it off and learn your lesson, which you did by fixing it so you can remember the next time it happens. As mama said to Forest Gump, "stupid is as stupid does," so remember that you are not stupid. However, having said that, it is fun to share our "DUH" moments so that we can all laugh at ourselves because we all know that we are not alone in makings silly mistakes.
Having done this a time or two (or ten) here is an easy way to remember which way you thread your needle:
There is a groove on your sewing machine needle, you can feel it with your finger nail. What ever side that groove is on, that is the side that your thread should go in. So no matter what machine you go to, even if you have never sewn on that machine before, you can always tell which way to put in the thread.
However, if you should forget which way your needle goes into the socket, when replacing the needle, you will need your sewing machine manual for that information. I've never looked, but I am hoping that it you put a mirror under the needle hole that you can see which side the flat part of the needle goes in, just in case you don't have your manual with you.
I usually keep my manual with the sewing machine at all times, even when I am transporting it to a class, just in case I need to know some information. There was a time when I didn't do this and found myself at a standstill trying to figure out something, when I could have been sewing. Unfortunately, I was in a class and because of this got way behind and didn't to fully participate in the class. Bummers -- a lesson I never forgot.