Currently, the only effect is has is to add a small warning icon like this https://mastodon.nzoss.nz/@rimu/111648660649299579 when reputation becomes < 0. At < -10 there are two warning icons. What people do with that information remains to be seen.
Reputation is the sum of all the up-votes they get, minus all the down-votes. That is the main factor. I doubt gif reactions will be a big influence.
Upvotes in meme communities do not increase reputation.