People who are using their cellphone/mobile as a telefon (calling someone) but not holding it as a telephone but as a slab in front of their face. And ofc with the speaker on.
Slightly better but still stupid: Videocalling (or Facetiming) with the phone right in front of their nose.
I mean, just hold the phone so that the speaker is at your ear and the mic is right by your mouth...
Not OP but the first three things I already experienced today were: Knee and backpain, standing out in a crowd, needing to slightly bend down vor everything in most standard kitchens.