It drives me potty! Secretively though, as my sister's kids, her husband, my friends children (in the main), and a number of my friends, all do it.
E.g: Baff/Bath....Fink/Think...Free/Three etc...
When I hear 'th's' dropped it makes my teeth itch. Also my 2.5 year old son does it, and my DH tells me off for trying to correct him.
He (my son) now wanders around the house saying 'baff/aff/aff'.
AIBU? Should I just let it go?