The result of committing repeated faggotry. Even if you have never had gaysex, you will still get Buttaids from the act of faggotry.
A breakthrough in recent research has also proven that it is possible to get the Buttaids from using Vista and Java, which also give the risk of contracting Javaids and Vistaids.
If you contract all three of the said diseases, you will become a Ubuntard.
Buttaids is a serious disease, and cannot be cured. Once you have it, it becomes a part of you forever.
"I has teh Buttaids!"