Why does it show that? I don't believe that I posted or did anything on that day, so I should not have lost any reputation.
-2 is usually linked to receiving a downvote on your question or post.
I searched your questions and answers for downvotes and only found one:
This is not the reason why you lost
2 reputation points. As @sathya mentioned above, the
-2 is linked to one of your deleted answers:
3 of your questions have been deleted. 1 of your answer has been deleted. Click on "show removed posts" at the bottom of the reputation tab to show this deleted post.