Fatal Flaw...

I think we all have one trait/quality that is a little less endearing than the other wonderful qualities we possess.
My fatal flaw?

Keeping my mouth shut.

I just sometimes lack the inability to filter my comments and actually keep my mouth closed. Especially when it involves other people. I tend to speak before thinking. I like to think it's because I spend 8 hours a day using my filter in hypersensitive mode. You know, not actually commenting when a child is hurling expletives in your face or when they tell you something that is completely ridiculous you can't help but snicker. However, I'm leaning towards it not having anything to do with hypersensitive filter mode being on Monday-Friday 8-5. I think this because I can recall numerous occasions when my mother had to quietly remind me to think before I speak.

My fatal flaw was in full effect last night at my CPR training. I went to use the bathroom and posted on the wall of the stall was a urine chart. Said chart had different shades of yellow describing urine and which levels showed hydration and at what point you might be dehydrated, ending in a color that simply said, "contact your physician". I was laughing with another trainee as we gave number values for our pee.

We walked back to training and I was chatting it up with the trainer and mentioned the absurdity of the urine chart and how I couldn't refrain from laughing. She looked at me and simply said, "That was my PhD project." Enough said. Apparently it's not funny to the author. As a result, I did a little back-tracking and had to quietly retreat to my seat before making an even bigger @$$ of myself.

Oi vey. Open mouth, insert foot.

What's your  fatal flaw?