A memefail denotes the occasion when your complete ineptitude at finding an appropriate meme in particular, and at life in general, stares you in the face and you hate yer existence. Alternatively, a memefail can also be used to refer to the inept subject who is a general failure at life.
Mr. Dundleby, your memefails are so ridiculous, you shouldn't be allowed anywhere near memes. Like ever.
Rhonda's such a memefail, and not just on the internet.
Adding an obvious and uninspired meme to another person's joke or post, thereby riding on the coattails of their humor/insight/story for upvotes, likes, etc, without making a genuine contribution.
When that redditor added an "Everyone liked that" meme to a feel-good post about a loyal dog, he was just memetailing and won't get an upvote from me