I propose 2 new tags, male solo, and female solo. The current solo tag isn't ever used, and these are improvements for the tag to be more specific and people should use these new ones.
Right now if a straight male blacklists the gay tag, they will still see posts that are solo male. This works under the logic that the solo male in the art may not be gay in sexual orientation, gay in this case isn't about the viewer's sexual orientation, who would not want to view a male solo post. Basically, if someone blacklists gay, they will still see art that is for gays.
But right now there is no tag for straight males to use to blacklist male solo pictures. These new tags will fix this.
This is just one specific example of the use of this tag.
Basically, this is useful for people who want to search for solo pics of a specific gender, or want to avoid solo pics of a specific gender.
Updated by NevanNedall