The term has come to mean the following:
to ether oneself.
Now, to ether in the art of rap music has come to mean to diss someone so severely that the disrespected person's career is never the same, or totally over. The term ether originates from Nas's diss track of Jay-Z (even though Jay-Z's career remains strong).
To ether oneself, though, is entirely different. In this case, one would release a diss track towards another person expecting to ether them. But instead, the diss track is so bad and disliked, the artist who made the diss track is forced to end his own career.
In the much broader sense of the term, 'goulish' can simply mean to end one's own career without having the intention of doing so.
So, now, instead of saying 'Frank ether'd himself', a person would use the term "goulish'd."
The term can be spelled "goulish'd" or "goulished."