Much like a kitten plays with a yarn of wool, batting it around in fascination, the young male smacks the old bat's boobs however he likes
It is also when an old lady wants to get a bit frisky and use her saggy boobs to smack a young male's gob or other parts of his body.
Old lady: Oh darling you wouldn't believe how well that 20 year old gobsmacked me last night, it was delightful!
2. To be hit forceably in the mouth.
Seeing that water skiing squirrel has left me gob smacked!
2. I got my gob smacked last night when I gave my woman a dirty sanchez.