It bothers me when someone starts a sentence with "UMM." I don't care that "umm" is the first word out of your mouth, I care that you've put so much emphasis on it, and assaulted my earholes with your derpitude.
"UMM, I disagree with your hypothesis."
"UMM, no, I'm not really hungry right now."
And my personal favorite, "UMMMMMMMMMM, let me think about it."
NO. You do not get to "think about it" and yell at me at the same time. Pick one or the other, buddy. You're making my brain bleed.