Inefficiency drives me crazy. It's both my best and hardest quality.
On one hand, it's what keeps me moving forward without stopping, because there's always something to optimize, always a way to make it better. Whether it's a product, a design, or an internal workflow.
On the other hand, it means I never settle. I give feedback constantly, I always push for better - and yes, I know that sounds like "my biggest flaw is that I'm a perfectionist," but what I'm actually saying is: I'm not the right fit for every team or every person. Only for the ones who move fast, keep improving, and never stop being hungry for it.
Oh, and people tell me I'm fun to work with.