When someone has no sexual preference and can not be defined by being gay or straight.
There is no parade for a slagsexual, unless you count the solo walk home on Sunday mornings.
"What she's sleeping with Annie now? I did not know she was gay."
"Oh she's not gay or straight, she's just slagsexual. She sleeps with everybody."
A woman who "claims" she is bisexual but has never been in a relationship with another woman and just makes out with her "girlfriend's" to get the men turned on when they are around thus getting sexual attention. This gives a bad name to people who are real bisexual's.