In a club/bar I surprisingly often come across the following scenario: cute tipsy girl seems into me and we hit it off. Next to her is a not so cute "best friend" girl who is clearly sober with a cold frown all over her. When the cute girl is not looking she will come over to discourage my further advanced with some clearly made up bullshit like "she is married" (it is clearly bullshit because when I politely ask about this husband she stumbles trying to invent a name and location etc). My question is, why is the frowny friend doing this, and how can I handle it well?