Christopher, I love the curious and thoughtful nature of the questions you post and of your approach overall.
If I'm not practicing metta here, then I'm just flapping my proverbial gums. If I feel annoyance, then there's all the more reason to be mindful of it and make an intentional choice about how to proceed rather than blindly swirling in the downward spiral of the twelve links of dependent origination (rather than the upward spiral of Transcendental Dependent Arising).
There isn't a single time that I feel annoyance that I'm not clinging to something, most often to views. Annoyance cannot persist in the absence of clinging. Even if I find myself in opposition to someone's expressed view or to their overall style of interpreting the Dhamma, there is also the choice to recognize that every single person on this forum is seeking to eliminate suffering and experience happiness (as are all sentient beings). If I'm responding to someone (or even thinking about someone in the absence of responding) and I'm not doing it from a place of metta, then what am I really accomplishing? It's more downward spiral, which is contrary to the purpose of participating here. There's a difference between spinning our wheels and turning of the wheel.
It's truly walking the razor's edge, as it were, neither suppressing annoyance nor indulging it, but instead watching it with as much mindfulness, equanimity, and compassion as I can muster. From that point, thinking and responding with metta is much more possible.
One of my favorite teachers is Christina Feldman, who said, "The quality of mindfulness is imbued with warmth, compassion, and interest. In the light of this engaged attention we discover it is impossible to hate or fear anything or anyone we truly understand."