How would you react to a woman starting a gross rumor about your husband and son

My son is 17 and while he's close with both of us. He is and has always been a daddies boy. They have a very close relationship and he will typically go to his dad about something, especially with relationships and sex, before he comes to me. He also has a pretty crude sense of humor that my husband matches.

Example: We were all volunteering with a blood drive. They had all the volunteers meet up and we did team building stuff. One was an all about me and they asked what was your favorite toy? My son wasn't the only one who it sexual but he said "Hey dad! Is dildo spelled with one L or 2!" My husband just said "One!" Everyone laughed. I died inside a bit. Last year he said it was the cigarettes his dad used to burn him as a child (That didn't happen. He was being a ham) but that's just there relationship.

Some women started a weird rumor that they're having sex and I know who started it. It's someone that I considered I had a friendly relationship with. That is a complete lie and I have proof she's been spreading that around. She's not spreading it in a way that is like "I'm concerned about child SA." She's spreading it around like hot gossip. Also nothing is going on. That's not true. She just decided to spread that around

@Mrs as I said he wasn't the only person who made it sexual. One woman was like "I should put my rose(a virbator). I probably should have added 90% of the people volunteering were friends. We all knew each other. They all make jokes like that. A lot of them knew my son since he was in elementary school. A lot of people at that meeting were making crude jokes. That's why he felt like it was okay for him to make a crude joke.

@Hannah again a lot of them made the "favorite toy" joke sexual. They also know our family and know my husband and my son's sense of humor. This wasn't at the blood drive. It was all us volunteers together for team building stuff but I already know most of them. Someone said they wanted to put down their rose. Someone said their husband husband's favorite is their strap on. A lot of people made that part sexual.