I don't have any specific one. To me any character traits can be a defect, even the generally speaking the favorable traits such as gentleness, can be situationally a defect.
IMO every characteristics and personalities are two-edged sword, the only difference is that is it the blade or the back being sharper/blunter.
Therefore, in order to write about the so-called character defect, I like to put them in situations where their personalities or characteristics traits are not needed to solve the problem, or they are just worsening the problem further. So they need to step themselves out of the comfort zone and adapt to a different way of dealing a problem.
Well I won't really called myself as any characterization-savvy, because it is not like I had wrote thousands of story nor created thousands of different original characters to gain understand of that.
It is not a specific character trait, but there is one specific character in my current fic that is just generally speaking full of defects, and he is my favourite. He suffers from emotional disorder, unable to feel happiness, but yet because he can becomes negatively emotional, he acts irrationally for quite many times, slandered by many people as being "The walking hazard", no one wants to get close to him. As this story I wrote in 1st person narrative, looking at this character from the eyes of his closest relative just makes me thinks a lot about the negative characteristics traits where the public all deemed to be "defects".