You're the owner of the building which has 13 apartments

After a few months, 3 specifically, it's time to collect the rent from your tenants, so you start to knock on each door to collect the rent from each of them. Slowly you finally reach the last apartment in the third floor, the last tenant. You raise your fist and firmly knock at the door

After a few seconds, she opens the door, wearing a revealing night dress, she tiredly looks at the wall before looking you, as her usual...

"Oh.. I didn't notice you.. you're... uhh.. who are you...?"