I think it's important to note that elementary particle-antiparticle collisions can only result in an annihilation if they are of the same type. This is pretty much by definition, otherwise some conservation law (conservation of electric charge, for example) would be violated, which would not allow the process.
Scattering of composite particles, such as hadrons, would boil down to the logic described above.
You have reactions like ##K_s \to \gamma \gamma##. A rare decay, but still possible (and measured). The same should be possible for D0, B0 and Bs, but there are just upper limits. All those decays are similar to quark/antiquark annihilation with different quark types.
See also This paper for theory predictions.
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