I’ll go first: lipstick. Even when my lips don’t seem chapped, little bits start to come off as soon as I apply matte lipstick. Plus, I often don’t like the look of gloss.
EDIT: 
Winged liner seems to be the top answer here???
Winged eyeliner is still a struggle for me. My left eye ends up with a thin, pointed wing that looks great, but my right eye always turns into a chunky, rounded mess.
I’ve decided to embrace the messy look of pencil eyeliner and a bit of dark brown eyeshadow because I can’t be bothered to do anything neat! Hopefully, it looks intentional at this point.
I’ve switched to black powder under my eyes & a thin line on the top lid. My eyes are already big, but that combo makes them look even bigger.
I just can’t figure out how to apply fake eyelashes, no matter how many times I try…
I’ve been wearing fake lashes for years, and I still can’t stop them from lifting at the corners, no matter what techniques, hacks, or glue I use.
I finally got fed up with Glamnetic and started getting extensions a couple of months ago. I LOVE them! They look amazing, and I can be ready in 5 minutes if needed.
If I didn’t have to deal with the maintenance, I’d love to get extensions.
Lipliner and eyeliner are my biggest challenges. I have a faded birthmark on my top right lip, so I’m trying to create a lip line where I can’t see the border. Plus, I think I have slightly hooded eyes, which makes applying eyeliner a real pain.
I have the same problem due to a scar on my lip. Plus, my lips are crooked because of my teeth. 
And to top it off, I have heavily hooded eyes. It’s rough, lol.
I usually skip lip liner and opt for a blurred lip look with lip stain since lip liner is a struggle for me. I also have hooded eye makeup tutorials saved for reference. Smitha Deepak is my go-to YouTuber because her tutorials are actually achievable in my experience.