Well, once my ex - gf's mom was really strict. She always had a lot of rules for my ex - gf. For example, she had a curfew for her even when she was in college. It often led to some arguments between my ex - gf and her mom.
The most immediate consequence would be the destruction of your relationship with your girlfriend. She would likely feel extremely betrayed and angry. It could also lead to a rift within the family, causing a great deal of emotional pain for all involved.
Definitely not. In most cultures and societies, there are clear boundaries within relationships. Having sexual relations with your girlfriend's mother is not only morally wrong but can also cause irreparable damage to many relationships, including the relationship with your girlfriend, her family, and your own self - respect.
Oh, that's an awkward situation. Maybe it was a case of someone waking up confused in the wrong bed and realizing it was their mom instead of their girlfriend. It could have been a situation where in the dark or in a sleepy daze, the person made a wrong assumption about the person in the bed. For example, if they were visiting their parents' place and had a late night, and their old habits of being at home made them end up in the wrong room.
Communication is key. The gf should be open and honest with the mom, and vice versa. For example, if the gf has certain habits or beliefs, she should share them with the mom in a respectful way. And the mom should also be receptive to the gf's ideas. By talking regularly, they can understand each other better.
The first consequence could be extreme embarrassment. Just thinking about it would make the person blush. There could also be a strain on the relationship with the mom, as it's a very awkward situation to be in. And if the girlfriend found out, it could lead to some trust issues in that relationship as well.
One possible plot could be that the mom really likes a girl she knows, like a daughter of a friend. She then tries to set up her son with this girl. She might arrange a lot of 'accidental' meetings, or constantly talk about the girl's good qualities to her son until finally, the son starts to consider the girl as a potential girlfriend.
It can end well if the son and the girl actually start to like each other for real. Maybe at first they were reluctant because of the mom's forcing, but as they spend more time together, they discover they have a lot in common and fall in love.
In such fantasy stories about blackmailing a girlfriend's mom, a prevalent theme could be manipulation. The blackmailer tries to manipulate the situation to their advantage. Also, the theme of family drama might be present. The situation might be presented as a complex web of family relationships where the blackmail is used as a tool to disrupt or control. But we must remember that these are just fictional concepts and should not be emulated in real - life relationships as they are highly unethical.