There’s a series of episodes in the current season of “Shameless” in which man-bunned hipsters begin to embrace The Alibi Room — a neighborhood dive bar in a down-and-out Chicago suburb. The ironic twist arrives when the bar actually starts to not only embrace its new audience, but even put up a banner trumpeting: “Voted the S**TTIEST BAR in Chicago.” Ironically, no sooner does The Alibi begin this half-hearted marketing attempt before the hipsters move on, largely because the venue has become too mainstream and has lost its original sad-sack ambience.

As a plotline, it’s not just an insight into the Millennial market. It’s also a kind of cautionary tale for the beer brand, Pabst Blue Ribbon, or PBR.

Everyone knows the brand soared to prominence since seizing cult status around 1979 — so much so that, when it was put up for sale in 2014, its value was estimated around $1 billion. For awhile, at least, the brand was the fastest-growing domestic beer of the last decade.

When we dig in, we can unearth a few truths about its success. It represented authenticity and the appearance of being completely unrelated to anything corporate. Bike messengers — a counter-cultural caste if ever there were one — were one of the original social niches to embrace it, and PBR capitalized on their loyalty with event marketing, such as bike rodeos. The brand also appealed to artists to produce Pabst-themed work, a tactic it continues today. Before long, PBR became a subcultural darling, with an allure that inevitably spread to more mainstream audiences, like yuppies.

But those glory days may be fast fading.

Ever since 2009, PBR sales have flattened precipitously, even as the economy recovered. One reason is that loyalists have migrated to heritage beers, such as 125-year-old Narragansett, which offers broader flavor varieties. Another is that even dive bars now offer local-only craft brews. Perhaps the most cogent rationale is that, when everybody’s poor, it’s cool to be cheap. But, as Millennials gain their financial footing, cheap can begin to look simply desperate.

As marketers, there’s wisdom to be gained from this brand’s trajectory: even a “discovery brand” that rockets to success may eventually need to adapt to the market. The trick is knowing exactly when you’ve outstayed your welcome.