My wife works in copyright and image compliance.
@fast-electrician-95402 is right in that memes exist in a gray area. While not technically fair use, it is generally agreed that if it went to a judge they may see it as such so no one has taken the risk of pursuing it yet. If you're sharing memes that other people have made, you're more likely to get away with it even though even sharing a meme with infringed copyrighted material is infringement. If you are creating the meme and using copyrighted material to do so you are infringing and could get caught.
She has settled cases against infringers who have created a meme. In that instance, the person stole an image from a photographer and added text overlay.
Also, there's the case of
Shepard Fairey vs AP. Not only was he guilty but he was
the only person to get criminally charged. If something is already in the public zeitgeist, like that Patrick meme, it's fine. But don't take a photo from somewhere, add text, and claim it's a meme. It'll backfire.