Prosecco Stormfront means: The British parenting-focused message board Mumsnet, viewed as a locus of gender-critical discourse and activism.. It is internet-era slang, commonly seen on TikTok, Discord, Reddit or X. It is generally derogatory or offensive; worth a quiet word about how it lands on the person being described. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.