There's a feedback form here
imgflip.com/about where you can report any sort of activity.
Or you could always make a meme for imgflip stream and the mods will find it.
However, I can already tell you what their answer's gonna probably be. As long as a stream is contributing positively to the community it's highly doubtful it's gonna be deleted, in my opinion.
There was a movement to consolidate all the positivity streams into Peace_On_ImgFlip, and I think it had some success, but I still see new anti-bullying streams pop up every now and then.
Let a thousand streams bloom seems to be the approach.