HBO and Drybar got much bigger response than they bargained for when the pay cabler and blowout salon franchise partnered on a marketing campaign for the second-season debuts of “Girls” and “Enlightened.”

In an email blasted last Thursday to its clients, Drybar heralded the HBO Happy Hour, where free blowouts would be offered “compliments of HBO” at any of the salon’s nationwide locations Friday through Sunday from 6-7 p.m. to “celebrate” Sunday’s return of the two series on HBO.

Typically, the salon chain offers a hair wash and styling session for around $35. “No cuts. No color. Just blowouts.” is the company slogan. Since the first Drybar opened in Los Angeles in 2011, the salon has blossomed into a national franchise with a dozen outlets (and counting) in California, five in New York as well as outposts in Atlanta, Houston, Phoenix and other cities.

With HBO willing to foot a salon bill that would, by Variety’s math, easily soar to tens of thousands of dollars, Drybar devotees took to the Web and smartphones to book appointments — only to be stopped in their stiletto tracks by overwhelming demand.

The Drybar appointment booking site crashed as throngs of femmes attempted to book their free HBO blowouts, setting off a small social-media firestorm that quickly transformed the excitement about the promo campaign to frustration about the inability to find any salon with an opening during the qualifying hours. The reality plaguing the promo campaign was that, given the number of chairs at each of the 25 or so salons, Drybar could accommodate only about 500 clients for HBO Happy Hour.

The love for Drybar blowouts and HBO’s femme-centric shows, of course, greatly exceeds that number.

A few hours after the Drybar-HBO partnership announcement, Drybar founder Alli Webb sent an apology email to her clients.

“Unfortunately, despite staffing up our phone receptionists for this promotion, we dramatically underestimated the response here and are terribly sorry for any inconvenience,” Webb’s email read. “I truly feel awful … we will do a better job of planning next time, I promise.”

Sounds just like something Hannah would say, doesn’t it?