my mother-in-law's habit (and, yes, she passed it down to her daughter) of interrupting conversations with things that absolutely don't need to be said.. or things that don't need to be talked about right now.
you can be engaged in a 1:1 conversation with, for example, a cop about an accident you just witnessed and this lunatic will walk up, get your attention with a "hey" and then commence to tell you about her lawnmower that isn't working and how she needs your help taking it to the shop. completely ignoring the fact that you're trying to talk to someone else, about something totally unrelated to what she just said, that's actually important.
i'm not 100% convinced it's malicious or manipulative... it always feels more that she's just completely oblivious. like she has such narcissistic tunnel vision that she actually physically cannot see anyone other than the target of her monologue.
had soccer last night. hot, hot and humid. no subs. middle of the 4th quarter (no halves) one of the kids threw up and came wobbling to the sideline. i benched her right away got her a Gatorade and some ice and told her to get in the shade. then post-game walked over to talk to her mom.. who happened to be sitting next to my wife... to let her know what happened, etc. mid explanation, my wife, who is sitting there listening to me, says loudly "well, we have a huge problem..... it's the fence guy.... i need you to help make a decision or we could really be screwed."
double take, triple take... what?
i give her a confused and angry look and say "...........are you serious right now? i'm telling this girl's mom that she threw up mid-game.. that her (black) daughter looked pale, said she was dizzy and not feeling well and you interrupted me to tell me we have a problem with the fence guy????? that can't wait 3 minutes????? now you tell me??"
wife:

(undaunted) but i need your opinion before he shows up
tomorrow morning
me: (attempting to maintain composure) i'm not talking about that right now. (girl) could need to see a doctor here. i'm trying to tell her mom what happened and what i saw so she can make a decision on something more important than our fence. the fence can wait.
wife:

you're being rude!
me: ####
GOOD TIMES!