Two people that meet for the sole purpose of a work out. One partner usually knows enough about fitness and sports to help the other develop physically and meet a personal goal. An unemotional, homogeneous association between two people without a need for friendship.
John and Jane meet at the gym once weekly to work up a good sweat. They are sweat buddies.
I like to be with my sweat buddy when I workout because I hear positive karma about the future outcome of my sweat work.
Being sweat buddies is much less complex than being friends.
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi