As bored as a bat on Sunday

[marcopront]

My daughter miss heard me and thought I had said "As bored as a bat on Sunday" I actually said "boarders are back on Sunday".

We really like it as an expression but can't think of a reason for it. So

1. Can you help us make up an explanation for it.

2. If you like it, use it.

Well, Bat's often just hang round with nothing better to do so are probably feeling bored and Caves might be quieter on Sundays than the rest of the week

"bored as a bat?" SOunds great!