I can’t remember when has this started but it seems you can only see positive reputation changes in chat now. I want to know if this is happening to everyone or just me before I submit it as a bug report.
I just ran out to Stranglethorn and smacked some pirates. The rep decrease showed up in the chat normally. (Both with ElvUI and all addons disabled.) Have you checked your chat settings to make sure they are showing rep? What were you doing that should have shown a rep decrease?