In English the word bag sounds a little bit like bad, dad and back.
A dad joke is normally a very bad joke that fathers tell topically but not exclusively on a long family holiday, when the family is stuck with the dad and have no plausible way to avoid the joke.
Dad jokes are not only told by fathers, of course, and a good dad joke, when timed well and delivered with sufficient conviction and charm, doesn’t necessarily have to be dad… I mean: bad 🙂 There are plenty of good dad jokes out there, I’m told.
The joke on the I’ll-be-bagbag is particularly good because it plays with the similarity of the words: bag, bad, dad and back. I love it and thank you for it people at Scholz :). ‚I’ll be bag‘ is an obvious a reference to the famous quote from the Terminator films, but to reduce it to just that, wouldn’t give this finely layered humour the justice it deserves.