Yes I stole this thread idea from gaf, but I thought it'd be interesting.
I have a bunch of these.
Let's see, last night my friend was singing Amazing Grace quietly while my circle of friends and I were all laughing and talking. He's a terrible singer, so I jokingly said "Jon, I love you, but you can stop now."
The room got all quiet, and so did he, and he looked very serious.
I'm guessing he took it personally. >.> oops
Also, last year someone wished me Happy Birthday and I said "you too" back to them out loud. :x
Ohhhhh and I'll never forget this.
In 8th grade I jokingly replied to someone asking where something was by saying "It's right thurr" like Chingy's song Right Thurr.
Everyone stopped and looked at me and teased/laughed at me.
I didn't realize why until I figured out that I was essentially talking like a "gangsta" when I was the whitest kid in the room.
Also, I sometimes repeat myself or ask the same questions in idle chit-chat because I'm not paying attention.
Me: Hey how are you doing?
Them: Im fine, how are you?
Me: Im good, and yourself?
EDIT: Oh yeah, commented on a girl's picture on Facebook last year, saying I thought she was pregnant.
It was very awkward.
We haven't spoken since.