They're best friend. One might thought they're enemies by the way they act around each other but that's just the way they showed their brotherly 'love'. Kicking, smacking, loads of insults you name it. Jongin was really sure kissing never appeared in their dictionary but as Kyungsoo said 'we'll never know what fate has in store' and Jongin really don't want to know his fate if his hunch about his best friend turns out to be real.