Sharing this kind of story is not acceptable. Intimacy within a marriage is a private matter. It violates the privacy and respect that should be maintained in a relationship and in society in general.
No, it's not appropriate. Such stories are very private and personal aspects of a relationship. Sharing them publicly violates the privacy and dignity of the relationship and can make others uncomfortable.
The main ethical problem is the lack of respect for privacy. Everyone has the right to keep their intimate life private. Spreading such a story also shows a lack of respect for the wife as an individual. It's not just about sex but about treating people with dignity. In addition, it can have a negative impact on those who hear it, as it is inappropriate and vulgar content.
If you trust your wife, you can take it as a positive thing. She might be showing kindness or gratitude to him for some help he has given. You could also join in and say something nice to him about the bouquet.
It is not appropriate at all. This kind of story belongs to the realm of inappropriate and private behavior. In a civilized society, we should focus on positive, respectful and ethical topics.
Politely distance oneself from the situation and the person sharing it. Maybe change the topic if possible. There's no need to engage further as it's an inappropriate topic.