Lol — there is only one creature on Imgflip more tiresome than the upvote beggar. And that is the non-upvote giver shamer. :)
Yes, it’s considered polite to upvote comments. But sometimes you are busy. Sometimes you just forget. Sometimes you just don’t agree with the other person’s point or they’re literally actively dissing you. All excusable or valid reasons not to upvote (and tbh, the promoters of this facet of Imgflip etiquette do the same).