Classic rock is about heavy hooks, power chords and tight harmonies. But it’s also about letting loose and enjoying the good times. And there’s no better time for that than Friday evening, when we pick up our paycheck, punch out of work and enjoy a couple days of much-needed rest and relaxation.

This week, we pay tribute to an early breakthrough for a group of Scottish rock gods who helped define blue-collar hard rock during the '70s and continued to slog it out on the road for decades, even as their commercial fortunes dwindled. The song in question? Nazareth's 'Hair of the Dog,' a grinding anthem about the battle of the sexes whose take-no-prisoners attitude boils down to the oft-quoted chorus tagline "Now you're messing with a son of a bitch."

Even though the song -- which served as the title track to the band's sixth album, released in April 1975 -- shares its name with a folk remedy for hangovers, the title is really a play on words. The band originally wanted to call the album 'Son of a Bitch,' but for obvious reasons, its label interfered. As singer Dan McCafferty recalled in an interview with Classic Rock Revisited, "The record company went ape s—. They said, ‘You can’t say that.’ We said, ‘F— off, John Wayne says that in his movies, and he is the neatest thing that you’ve got going.’"

McCafferty's argument fell on deaf ears, so the band decided to go a subtler route and title the album 'Heir of the Dog.' But after printing up a small number of copies (which went on to fetch obscene prices on the collector's market), they mandated another switch, forcing the group to finally settle on the more traditional spelling. But as it turned out, all those behind-the-scenes shenanigans couldn't stop 'Hair of the Dog' from breaking the band through to a worldwide audience.

Not only was the title track a sizable hit, but the album also spun off a huge pop smash with Nazareth's cover of the Felice and Boudleaux Bryant classic 'Love Hurts,' which went on to become the most widely known version of a song already covered by the Everly Brothers, Roy Orbison and Gram Parsons with Emmylou Harris (not to mention Traffic's Jim Capaldi, who released his own 'Love Hurts' cover the same year Nazareth's came out).

While 'Love Hurts' probably paid a few bills for the band members over the years, it's 'Hair of the Dog' you'll more likely want to be listening to after clocking out of work on Friday. With its driving beat (dig that cowbell!), dirty guitars and McCafferty's screeching vocals (and talkbox solo) topping it all off, it's the perfect soundtrack for a night of troublemaking -- preferably while blasting out of the jukebox at your friendly neighborhood bar. There's a reason 'Hair of the Dog' has been a favorite for many of the bands that followed in Nazareth's footsteps, including Guns N' Roses, who covered the song on their 'Spaghetti Incident?' LP: It's fun to listen to, fun to play and it oozes rock 'n' roll attitude.

Sadly, after 45 years with the band, health woes forced McCafferty to announce his retirement this week. The road won't be the same without this particular son of a bitch messin' with it, but in honor of his many decades of service to rock fans everywhere, we recommend playing 'Hair of the Dog' loud and proud this weekend. In fact, why wait for closing time? Just scroll up to the top of the post, hit 'play' on that video above, turn up your volume and let the weekend start now.

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