All of these are great ice breakers that can lead to more fun.
* My wife has answered the door for Door Dash and UberEats while totally naked. She will sometimes when it is a male driver accidentally drop the receipt and bend over to pick it up to ensure they get a full money shot view.
* We did an in-room dining meal at a Marriott hotel a few years ago. I let the server into our room while my wife was being fucked on the bed by a guy we picked up that night. I told him my wife would be done in a few minutes and we would all be ready to eat. The room service guy seemed to enjoy the show as much as I did.
* You mention your gf being naked when you return home with a friend like she was not aware he was returning with you. We have done that several times with a lot of success.
Here was my wife in one of those nights.
My wife was all in for this one, she was naked and sitting on the bed when I walked in with a friend from work. She was in front of a mirror as if she was in her own space unaware of our visitor. I called her on the way home (as our sign that I would be home in ten minutes so she could be ready) but she didn't answer so it all seemed totally innocent and random to the friend. When we walked into the room he was apologizing but my wife acted shy but then got up and told him she guessed he had already saw her naked so no use in hiding herself now.
Here are a few that have worked well for us that you might want to give a try. We have done it a few times and always with the same results. HOT SEX!
My wife had the hots for a young guy in our neighborhood and he openly would get erections when he was over around my wife. I invited him over one evening for dinner and he gladly accepted. After dinner, we sat in our family room talking and my wife suggested playing a game of "Adult Truth or Dare" on her phone. The game had setting you could select and it moved pretty quickly to where my wife was naked and soon following, performing sexual tasks. This young man fucked her three times that night and then regularly for the next three years.
Another young man in our neighborhood was over for a beer and my wife said she wanted to learn to play poker and asked if he could help her learn. He said he could and asked why she wanted to learn. She told him she wanted to play strip poker with a friend of mine but didn't want to not know what she was doing. I suggested they play strip poker to learn and the guy ended up fucking my wife several times over that summer. It always started with strip poker for them.
One night we were at a bar and my wife was dressed very slutty. She played pool with a few guys and then bet one young guy a drink. She lost and told the guy to join us and she would buy his next drink. While we sat talking the guy was coming on to her and said, "If you weren't married, I would love to take you home and fuck you silly." My wife just smiled and replied that if he could get her panties off, he could come home with us and do anything he wanted. He crawled under the table and came back up with her thong around his neck. The bartender kicked us all out, but my wife delivered on her promise and the guy got her to himself that entire night.