Crabs - Dad Joke - Fired.

[William51]

 Why are crabs so bad at sharing?.   Because they are always shellfish.                                                                                            When does a joke become a dad joke?.  When it becomes apparent.                                                                                          Why did the man from the calendar factory get fired?.   Because he was taking too many days off.

[Chipchopper]

When it's the same spelt backwards.