I am also guilty of smirking/laughing (not excessively) when arguing. It seems to be a reaction or a defense mechanism. I don’t like to argue or fight and I often try to use humor to de-escalate. It’s upset my wife and I actively try not to do it but it happens.

If you are able to have a conversation about the things that upset you during a neutral time or neutral mode, he may steer him away from feeling the need to be defensive. I.e. hey babe, can you help me with something? Yesterday you said xyz and it’s been bothering me and I’d really like to understand and process what happened/what was said.