To have an expressionless look on your face/Staring Blankly. The kind of look you have when you've spent the weekend on the razz and haven't slept a wink since thursday.
"What you upto today then?"
"mongin on the couch with a sunday face"
"good weekend then?"
"yeah...erm...I fink so"
The look on a persons face after having been deprived of sleep due to binge drinking/taking drugs.....usually after a good weekend.
"what's with the sunday face?"
"had a good weekend mate"
to make it an agreeable or less offensive expression in place of one that may offend or suggest something unpleasant to the listener.
It is an old expression but has been re-introduced in today's Urban
"I'm going to wash my sunday face"
"Don't touch my sunday face"
"Get out of my sunday face"