First, bosons aren't generally their own antiparticles. Hydrogen is a boson, and can annihilate with antihydrogen, but isn't identical with antihydrogen. It's also possible for fermions to be their own antiparticles, e.g. the hypothesized right-handed neutrinos. There aren't any special rules governing annihilations. The rule is that any interaction that doesn't violate any conservation laws will happen with some nonzero amplitude (the ["totalitarian principle"](https://en.wikipedia.org/wiki/Totalitarian_principle)). In relativistic quantum field theories, there's also a theorem that antiparticles exist with opposite values of all conserved quantities except energy-momentum. That means that if $a$ is some particle and $b$ is another particle with lower (perhaps zero) rest mass, then $a+\bar a \to b+\bar b$ (where the overbar denotes antiparticle) is always allowed. This includes, for instance, $2Z^0 \to 2γ$ or $2π^0 \to 2γ$ which could be called "self-annihilation" of identical bosons. (The $Z^0$ and $γ$ aren't directly coupled, but the totalitarian principle correctly says that the interaction can happen anyway – it's just not very likely.)