Aluminum Christmas Trees: a running gag involves Yanang (a city girl with no interest in plants that you can't eat, smoke, or ferment) not believing that certain plants (including wintergreen, mistletoe, and wolfsbane) are real-world life forms.
Asshole Victim: fairly common as victims of the more serious negative effects of Maenad's Aura of Weirdness.
Cool House: Maenad's mansion, in all its Gothic Revival, geometry-defying glory.
Cool Pet: a whole menagerie of them, ranging from tarantulas to peafowl to small sturgeon, but restricted to small-to-medium creatures who don't need extremely specialized living arrangements.
Lilja wants a dragon (or failing that, a pterodactyl), but has failed to find a reputable scientist who can make her one.
Creative Differences: one of the reasons Valerian left Imploded Aneurysm (the other was strained vocal cords). Val wanted to explore more fantastic and introspective themes and was beginning to cultivate her interest in weird religious imagery at the point that the other band members wanted to go Darker and Edgier.
Creepy Child: Violet Aciano was a mild example in her youth, due to odd mannerisms and an aura of eeriness rather than anything actually dangerous. Perhaps surprisingly, she grew up to be rather moe as an adult.
Cut Lex Luthor a Check: Magnus Ravnen actually earned the majority of his money through legal uses of his scientific talents, and viewed his supervillainy as a sort of combination of political activism and performance art.
"We all have our party together and burn a Yule log on the Solstice. It is a good central location, and everyone believes in astronomical events."
Expy: Valerian Nightshade, Musa Hawthorne, and Lilja Lakebetonika were fairly heavily inspired by Nathan Explosion, Pickles the drummer, and Skwisgaar Skwigelf of Dethklok.
Extranormal Institute: the boarding school Artemisia attended, which catered to the daughters of supervillains and people in similarly exotic occupations. They had classes in applied chemistry and "interrogation techniques" along with fencing and home ec.
Gargle Blaster: most of the cocktails Musa invents. For example, "Suicider," a little hard cider, apple brandy, Everclear, and cinnamon schnapps based concoction that tastes deceptively smooth for how strong it is, especially when it's served hot.
Genius Ditz: the girls in Maenad, although they don't all manifest it the same way, and the level of ditziness often depends on Rule of Funny.
Musa may count as a Ditzy Genius instead, as she's fairly book-smart.
Dude, Val would be awesome at that. She’d be like, "Hey, you want a copy of ''The Watchtower''?" and they’d be like, "Yes, please! Make it two! Just don’t hurt me!" and nobody’d dare tell her "GTFO I’m an atheist" because she’d… fucking eat ‘em.
Marshmallow Hell: Valerian is very tall, full-figured, and of a physically demonstrative nature, at least with close friends. This was probably bound to happen sooner or later.
Mistaken For Antisemite: for some reason, Violet's grandmother has developed the idea that all Scandinavian metal musicians (including Lilja) are Neo-Nazis. This makes things awkward when the band meet each other's families.
Real Person Fic: in-universe, Maenad gets some written about them. Valerian doesn't mind this, but she does wish that she didn't get slotted into the "abusive seme" and "fundamentalist homophobe" slots so often.
Satiating Sandwich: Yanang's "best sandwich ever," which consists of bacon, four kinds of chile peppers, spicy pickled fish fillets, curry mayonnaise, fried onions, fried garlic, kimchi, and radish sprouts, garnished with crumbled blue cheese, balsamic vinegar, and dried shrimp, and served on dark sourdough rye bread fried in bacon fat. She thinks it's awesome. Lilja is Squicked.
Seinfeldian Conversation: the conversation between Violet and Musa about what cleaning products from different countries would, theoretically, taste like.
Serious Business: anything that Maenad's involved in, between the "metal is Serious Business" crowd and the people who believe that the band have supernatural powers.
So Bad, It's Good: in-universe example: most of Maenad's non-musical creative endeavors. They wound up making a movie that was the cinematic equivalent of high-budget Author Appeal but turned out reasonably watchable due to a competent director and successful application of the Rule of Cool.
Artemisia and the Assassin are at about one and a half.
Pi would count as a one when just how hard he is to kill is taken into account.
Take That: Violet doesn't think much of Moe fandom. To be fair, when you already have problems being taken seriously as an adult "real musician" even by your closest friends, having your girlish innocence fetishized by strangers on the internet does not help.
Team Mom: Artemisia Mandrake (and occasionally Valerian) for Maenad.
Theme Naming: Maenad and many of the people around them (their manager, the producer they work with, the members of Musa's former band, their doctor, their shrink, and some of their family members) all have plant-themed names. All of Valerian's named exes (and several other minor characters) are named after bands. Most of the Mauve Shirt employees are named after One Woman Songs (or the male equivalent.)
There Are No Therapists: averted, although plenty of characters who probably need help still aren't getting it, and the one therapist to get much characterization has plenty of issues of her own.