Porno has it's place. We have all seen it, whether it was a private viewing for literal enjoyment or a public viewing for ironic enjoyment.
Hair Metal has it's place. We've all listened to it, whether it was a private airing for literall enjoyment or a public airing for ironic enjoyment.
Both porno and hair metal have legitimate value, both have an air of ridiculousness that can be laughed at. This is acceptable on all counts. The rule comes into play on *what* you find ridiculous about it. I'm sorry to say that while you may think you're original or witty for pointing out any of this ridiculousness, you are not the first, so if you are going to vocalize these ridiculousnesses in the effort to achieve a laugh from a crowd, be careful what you choose to Seinfeldize.
Pointing out the charming quirkiness of Hair Metal is as lame and played as pointing out the terrible acting and/or music in a porno movie.
Charming quirkinesses include: makeup thickness, hair height, spandex elasticity. If you look at a photo of Bret Michaels circa 1988 and exclaim: "OMG! Will you LOOK at his HAIR?" you might as well be saying "OMG! Will you LISTEN to that awful 70's PORNO MUSIC?" Do not laugh at these comments. They are not funny, these are established facts. It's not funny to point out that the sky is blue, it is not funny to point out that Hair Bands looked, in retrospect, quite absurd.