While Molly is pleased at being shown off a bit and it doesn't really bother her to be used as interception, she gives him a bit of a look.

"Oy," she says, even though she can't help but smirk a bit. "Don't be rude. Flirting with you probably would have been the highlight of her night."

Molly remembers not long ago when she was the one who was terribly, unsuccessfully trying to get Sherlock's attention and affections.