Meltdown fuel for my husband is someone interrupting him talking or doing a task, and a fast pace give and take conservation with a lot on the line.
On the surface both seem like BS excuses. My husband has an extremely hard time in give and take conversations. It's hard for him not to script in his head what he wants to say. At work, during a group meeting is horrible because of all these people talking, and trying to keep straight what everyone is saying or not (body language).
Interruptions because he can't switch his attention back and forth. He has a hard time just stopping and picking it up later. It takes so much concentration and effort for him to do a multistep task, that someone breaking that concentration enrages him. This can be anything from making Raman noodles to taxes.
Lesser stuff is bright sunshine and certain smells.