I have recently picked up the annoying (to me) habit of repeating the word "What?" when I ask it. It comes out as "What, what?" like I'm really anxious about whatever I just missed. But I noticed earlier this summer that my sister does this too, so my question is, did I pick this up from her? Or did she get it from me? Neither of our parents does it, so that's not the source.
I pick up little linguistic tics like that rather easily: for a while, I prefaced every opinion with "I feel like..." (something I still do on occasion, but not as regularly), a phrase I got from a college friend.