No this is not the start of a silly joke, but something that should really be in the game.

Why can't we knock on people's doors? The only option is to barge into someone's home through an unlocked door or commit a crime and pick the lock and enter.

If you are playing a reasonably good character, you would never just march into someone's home and start looking around even if the door was unlocked.

A number of times I have completed a quest and, when I return to the quest giver, they are at home and asleep in their bed. If you pick the lock to enter and attempt to speak with them, they get mad and threaten to call the guards......Ahem, remember me, the guy you sent into the dungeon to retrieve your family heirloom, I am just trying to return it as requested. It is also silly to have to wait 8 hours until daylight so that I can enter their home to finish the quest.

Wouldn't a nice feature be, upon targeting a door, to "knock"? It would allow you to awaken the occupents and complete the quest immediately. It would also be a more realistic method of encountering new people in cities. It just feels weird to walk into people's homes unannounced. Why not knock and have them answer the door to initiate a dialog? Some people may be polite and invite you in; others might stand at the door preventing you from entering (like in real life when some stranger knocks on my door). If it was late at night, they might say "go away, see me in the morning". If you were completing a quest, they would gladly let you in.

Yeah really.. Like have a little "conversation" style menue when you approach a door.. Press "E" (or whatever you have if your not on a PC) and be able to select like

"Open"
"Knock"
"Pick lock"
"Bash" (A really hard knock that would perhaps wake someone up and they be on a grumpy mood