My dad’s friend Ken married a woman named Roxanne when I was about 11. They played “Roxanne” as their first dance song. About four years later, when I knew what the song meant, I asked my dad about it. “Pleeeease tell me that they just used that song because it’s her first name!”
It was. Thank God! 
Soft Cell has a better inappropriate song than Tainted Love…Sex Dwarf - which is about the child porn industry.
(My friends all love Paradise by the Dashboard Lights at wedding receptions - I hate that song. My husband had to explain to the DJ that playing it would result in him not getting paid and us getting divorced.)
I’ll bet no one has nominated “Swamp Snake” by the Sensational Alex Harvey Band. The lyric goes “Let me be your swamp snake 'til the real one comes along…”
Also, “Dress Rehearsal Rag” by Leonard Cohen would be wonderfully inappropriate. It’s a song about a suicidal person prepping to kill himself but losing his nerve, as has happened many times before.
Two friends of mine in Montana decided to be married at the 1999-2000 millennium moment.
The bride, who regularly dressed in the style of Stevie Nicks, wished to walk down the aisle to “Landslide” by Fleetwood Mac. Apparently, the words “mountain”, “snow”, and “love” were enough for her.
In my opinion, the song is about love lost.
Of course, you don’t argue with the bride.
I once ate dinner across the street from an wedding reception at a local pub. They had your typical wedding band playing, and it took me a second to recognize Billy Idol’s “White Wedding.” When I left, they were covering “Girlfriend in a Coma.” That’s my kind of wedding reception!
What, not one mention of Stretched on Your Grave by Dead Can Dance?
The priests and the friars behold me in dread
Because I still love you, my love, and you’re dead
No, no, no - it was the work of Billy Connolly!
Joan Jett’s “I Hate Myself For Loving You” has to be on the list.
“Centrefold” by the J Geils Band if the groom really wants to piss off his in-laws. “Wicked Game” by Chris Isaak would be great for that also:
World was on fire, and no-one could save me but you
Strange what desire will make foolish people do
And from there it gets worse, as he sings about how he never wanted to love this evil woman.
If it’s a gay marriage, of course, you have to go with “I Fought The Law”…