Any variety of underpants where the buttocks are visible due to the fact the fabric has gathered into the butt crease revealing the cheeks.
Man these bumderpants are giving me an enormous wedgie!
These bumderpants keep riding up my ass crack - ouch!
I can see her bumderpants through that sheer skirt.
When some resigns or retires from a job, they are on "eternity leave". This can also refer to someone who has passed away, especially someone who worked somewhere for a long time, retired/resigned, then passed away later.
Oh I'm sorry, you didn't know that Kelly is on eternity leave? She resigned and moved to Hawaii!
With regrets I would like to inform you that my boss is officially on eternity leave. I will never see or hear them again. Ever.