My friend, a fat and self-conscious girl, mentioned ordering poutine and how good it was at BK: I blurted out "but not for you"...
Was having lunch with a friend whom was interested in me, made it obvious, yet also made it known early on that she had a boyfriend, but then said they broke up (both parts were a big lie overall). She was talking about some guy at her new office and how he was always hot/cold towards her. Conversation turned to me talking about some hot girl/friend at work who kept trying to get my attention despite having a boyfriend (relationship issues at time), and I said something about "WTF, she has a boyfriend, hell is she doing". Woops... So, I essentially called the girl I was having lunch with a slut. She gave me a dumbfounded face, but stayed quiet.
Related to the above, and not so much what I said, but what I did. Same girl, different lunch date a few months earlier. Only problem was I think she thought it was a "date", I just went to hang out. When I dropped her off at her building, she asked for a hug: I gave her a "friend" hug with one arm around the shoulder, one around the lower torso. She just stood there with a "WTF" expression on her face as I walked away. She would otherwise always initiate the hug with her arms around my neck. No, we don't talk anymore...