A Gelli

ge·lli also gel·li (gĕllĭ)

n. noun adj. adjective
1. An action that that could only be done by a Gelli. Usually incredibly unnatural, impractical, audacious, and humorous.
2. Speech that could only be uttered by a Gelli. Usually marked by no one knowing what it means and moving on and pretending to not have heard it.

3. To be a member of Horizontal Royalty, usually princess.

Probably from Arcadia An Gelli Ca, root of Raymundo, circa 1999.

Oh my god she just did a Gelli, now we have to deal with the consequences.
Oh no, please don't do a Gelli I cannot handle it.
After the Gelli was committed, no one was left alive.