To my point. The right side of my sink was backing up. I did what any dipshit would do and poured some gel drain fix down the pipe. Still backing up. The pipes were clear.
Now I know people in the "know" are probably figuring it out anyway. 3 words. Air admittance valve. It's a cap set up high that would be a plug if it didn't need to let air and water flow. The valve was stuck and was creating a vacuum. Plumbing isn't my wheelhouse and I was resigned to calling a plumber.
I took the cap off and cleaned it out nice then popped it back on. Smooth sailing now. Flowing perfectly. Dipshit confirmed, but I have that knowledge now. Afterwards I felt like berating someone and though of this scene...