No, blushing is most definitely not a disability. A disability is a recognized medical condition (e.g. there's a diagnosis for it) which has a greatly limiting affect on normal elements or activities of everyday life and which is beyond a person's effective control. Difficulties walking, visual or auditory impairment, nervous system or muscular disorders or diseases (e.g. Parkinson's, MS, MD), circulatory or pulmonary problems greatly limiting endurance, etc. are all disabilities. Blushing is not be, just as being physically unattractive is not a disability, tending to sweat more, a poor speaking voice, bad posture, or any other factor that could lead a particular employer to conclude you're not good at presentations. The fact that you suffer a detriment from something in one particular does not make something a disability, unfortunately.