I've noticed that if I talk to a certain friend a lot, I'll pick up on how they speak. Also, if I watch a bunch of interviews that a certain actor or musician does, I'll start speaking like them. I talk a lot like Allison Robertson from my favorite band The Donnas.
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Diagnosis: Major Depressive Affective Disorder, Generalized Anxiety Disorder, Mild PTSD, Agoraphobia with Panic Disorder, Attention Deficit Disorder of childhood with hyperactivity (more inattentive, though), Mild OCD, Social Phobia, Tourette's Syndrome