Anonymous wrote:So you and her brother find it, well, extremely cringe-making, and you say nothing to her?
How is his relationship with her otherwise? Your relationship with her? The fact you say she does other "cringey" things means these comments can't be totally out of character for her.
So your husband needs to say something. Not you--your husband, her brother. His sister is his to deal with. And since you don't indicate that she's awful in other ways, just stick with keeping it direct and somewhat light: "Whoa, sis, enough with the talk about your boobs and your milk. The kid's fed just fine, and I know you're just joking around, but both Wife and I aren't up for that kind of talk right out here in the coffee shop, OK?" Hearing from her brother fce to face might just give her pause more than if she hears that from you -- if you say it, she might fob it off as a joke, but -- unless your husband goes around loudly talking about boobs in public -- hearing him say that back at her might just get her to stop. At least for a while.
If she's the type who would get huffy and insulted and swan off saying, "Well! I was only playing!" just let it go and don't bring it up again -- until she does it again. Next time she holds the baby and starts in on the weird talk, find a reason to take baby back while changing to any other topic.
She is exactly that type, so we say nothing and laugh it off.
As far as other cringey things she says/does, I don't want to say anything too specific. But SIL has no qualms about talking very loudly and at length about her child's poops while out in public and when others are eating. She is in her mid 30s and dresses like a 20 something (booty shorts, low cut shirts and dresses, etc). She used to teach dance and had her 8 year old female students doing booty shaking, suggestive dance moves in their performances.
SIL's younger sister complained that my SIL was flirtatious with her new boyfriend when she brought him around, making comments like "It's hot outside, I could just walk around naked." SIL means well but is just very clueless how she comes off sometimes.