Words that start with "Th," "B," "P," and sometimes "T." "Th" especially beats me up and I usually don't win lol. But I'm speaking a language other than English, it depends on how nervous and anxious I'm feeling. I haven't noticed a pattern with certain letters or letters combinations with other languages. I stutter more with English though, and that's my mother language. I find it interesting how that works, where I stutter more with my native language than languages I learned later.