Mattress mermaid

1) A person (typically a female) that is content with laying with anyone on any bed with the intention of engaging in sexual acts; they are so content with doing the sex on any bed, because it's like their natural habitat.

That girl is a mattress mermaid, because she don't care whose bed she climbs into to get plowed.

The Wrong Mermaid

a. A merperson (usually a woman) who is the inverse of prevalent cultural depictions of merpeople: the front half of a fish attached at the waist to the bottom half of a person.
b. A sexual position based on this depiction, in which one partner is immobilized from the waist up, by tight swaddling with blankets.

Behind the door, I was shocked to find The Wrong Mermaid: Gwen immobilized on the couch, torso rolled tightly in Mom's quilt. Compromising as the position was, the back of Denise's head kept me from being forever traumatized by the sight of my pantsless sibling. I shut my eyes and pressed through to the hall.

Fickle Mermaid

The maneuver when you run for an office you are vastly unqualified for and refuse to share basic information about your personal income and policy positions with voters

Cynthia Nixon is really pulling a fickle mermaid with the people of New York