Male breasts, man boobs, often covered with hair. Floppy, allowing the dude to easily pass the pencil test. Decidedly unattractive.
Joe: Look at the tommyknockers on that jogger!
Sue: Eww! He should at least put on a shirt before going out in public.
* * * * *
Buffy: Ohmygawd! Our sweaty lawn guy has more cleavage than I do. His tommyknockers are bigger than my knockers!