To become attracted to or sexually aroused by intelligence and its use.
Me? I don't care too much about the plumbing. I want an incisive, inquisitive, insightful, irreverent mind. I want someone for whom philosophical discussion is foreplay. I want someone who sometimes makes me go ouch due to their wit and evil sense of humor. I want someone that I can reach out and touch randomly. I want someone I can cuddle with.
I decided all that means that I am sapiosexual.
Where the Dunning-Kruger effect and the bedroom collide. An alleged sexual orientation for people whose assessment of their own intelligence is far in excess of that of any reasonably objective observer, with the added benefit of making one a soi-disant minority, presumably an oppressed one.
People who describe themselves as "sapiosexual" usually define "intelligent" as "sharing my biases" rather than, you know, "intelligent". Given the first paragraph, this invariably means they're attracted to people as arrogant as them, who they run off with and have a clutch of horrible, spoilt children with who grow up into horrible narcissistic adults.
Furthermore, all it means is they're attracted to people similar to them, making the term fairly tautological to begin with.
In practice, "sapiosexuality" is in fact dickosexuality.