What should you do when you get frustrated because you just don't get it
1) educate yourself
I'm pretty bad at doing this. But thankfully museums know this about people and they provide a lot of educational materials so you can appreciate what they are showing you. Sometimes a gallery show will do this too. However, at gallery shows sometimes the artists don't want to tell you. They want you to see.
Thankfully google is in our pockets. You can google the gallery and the artist(s). Somewhere there will be an artist statement or an artist bio which will tell you a little about what you're looking at.
If you don't educate yourself you won't see that urinal as the statement that it was.
2) let it go
Each piece of art was not created for you. Artists often do not create to be liked. Even when the work is aesthetically pleasing it will not always appeal to everyone, nor should it.
But you don't have to the judge. It's freeing. Learn to recognize when art might just not be for you.
3) appreciate it
If something is beautiful and skillfully made it is easy to appreciate it.
It's okay to enjoy this art more.
It's harder when the artwork is stronger intellectually, emotionally or spiritually but not aesthetically beautiful.
Try to appreciate for a moment the bravery of another human being to spend their time, money and life to create something that will 9 out of 10 times be misunderstood and derided.
Conclusion
Years ago, I went to a museum exhibition that impacted me negatively. I didn't educate myself before hand and I'm not sure how much of the museum material I read. I got caught up on how I didn't understand the art at all. I was frustrated that they could call something so pointless and dark - art. It made me feel a spiritual darkness.
A lot of art is designed to impact us like that. Sometimes the artist wants us to feel a certain way or sometimes work is created from a dark place and so it has that impact unintentionally.
We don't have to accept it as truth just because it's in a museum. If art affects me like that I try to examine why. Maybe the artist did strike truth I need to examine or maybe not. Art is as complicated and varied as humans. Just remember, there is most likely a lot you don't know, it might not be made for you and some other human being had the bravery and fortitude to do something you didn't.