Meh'nday 

To be used when one simply does not care for Monday.

Meh Its Meh'nday!

Meh'nday by Adam Arcane February 8, 2010

Mehndays 

An overwhelming feeling of indifference that only occurs on Mondays.

Gregory:
How’s your day going?
Alyssa:
Meh.
Gregory:
Yep, you got a classic case of the Mehndays.

Mehndays by Geoffrable March 6, 2023