How to handle offhand observations by third parties - "Every time I see you, you're with a different girl"

Seeing as this is an unspecific question about an unspecific series of women, it's getting posted here and not in /r/askseddit:

What do you say when somebody says in front of a woman you've brought to a party or event...

"Every time I see you, you've got a different girl on your arm."

My date this time noticeably frowned.

"I'm sure that's not the case", I responded

but this drunk friend thought he'd inspire a debate, a conversational point even - so I changed the subject. It was the case wherein the last times I'd bumped into this friend had been other dates.

Sure a comment like this for some purposes could be great. But in the cases where it's not appropriate - like a girl who has an otherwise outstanding opinion of you, or who is chronically afraid of being a number...

What is the best way to handle a comment that makes you sound like a manslut?