Sarthusiasm 

A condensed version of being sarcastically enthusiastic.

Son: Dad look at my project!
Father: *sarcasm*Oh Wow!!!! That is incredible!!

Son: Wow Dad, thanks for the sarthusiasm

Sarthusiasm by Supermrgolf November 25, 2013

Sinthusiasm 

Having much enthusiasm for doing something bad or wrong.

The little boy showed much sinthusiasm when drawing on the wall.

The criminal felt sinthusiasm over his latest caper.

Sinthusiasm by SykoSuzie October 12, 2009