Take a screenshot of his latest and report it to staff. That's all you can really do (along with mentioning that the ability to abuse trophies needs to be fixed)
Trophy Abuse
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Why is there no way to turn off trophies? Look at the most recent one I've received from some idiot who's actually mad because I disabled people from being able to post on my profile notes.
How do I report such abuse? I'd of course much rather someone share a healthy debate with me in a thread rather than resort to measures like this when they're proven wrong.