Drinking coffee is like saying I reject the church. That is a thought I have daily as I drink my morning coffee. It’s cathartic, therapeutic, and energizing. Drinking coffee is an open act of rebellion.
Mormons are not permitted to drink coffee. It is against the word of wisdom. The word of wisdom forbids drinking coffee, tea & alcohol (or barley drinks). There is a long history of how it came to be a commandment when the original emphatically stated it was not by way of commandment. The current interpretation actually inverts some of the original and ignores much of it.

Drinking coffee is saying I reject Mormonism.
Besides the great taste and the level of normality drinking coffee brings to the human experience of today, it’s an act of rebellion. Drinking coffee is saying I reject the church, I reject the church teachings and I reject the church leaders. I disregard the so-called commandments and the “wisdom” of the leaders. I do not believe the Mormon prophets are inspired by revelation nor do I believe that the word of wisdom came from any god. Their proclamations include odd interpretations of outdated nonsensical dictation of Joseph Smith from during the temperance movement by a sexual predator. They interpret the dictation in the Doctrine & Covenants section 89 as meaning abstinence from certain caffeine drinks (but only the hot ones). The interpretation also leaves out many of the other points in the “revelation”, things like eating things in their season and eating meat sparingly.
The world accepts that caffeine is a nice pick-me-up found naturally in drinks like coffee and tea. The caffeine was so uplifting and pleasant, people began adding it to more drinks. But only the original caffeine drinks are forbidden by the church. Mormons can drink all the diet coke they want. It was even nearly blessed during a general conference.
It took a great deal of time, repetition, patience; no small amount of hope and faith; lots of reassurance from my wife; and many liters of a diet soda that shall remain nameless.
`O How Great the Plan of Our God!` General Conference October 2016
President Dieter F. Uchtdorf, Then Second Counselor in the First Presidency
https://www.churchofjesuschrist.org/study/general-conference/2016/10/o-how-great-the-plan-of-our-god?lang=eng#p13
Outlawing coffee and tea is a silly cultural peculiarity. There are debates about if it’s caffeine or if it’s certain acids or other ingredients that make it “unwise” to drink. It’s really a litmus test for how much the church can control its members. How blindly will they follow the tests of faith presented to them? What will they do? There are many examples showing that you can’t be mormon and drink coffee. You can’t go to Mormon heaven if you drink coffee according to this general conference talk:
Benefits of Coffee

As for me and my house, we will serve coffee. We reject the preposterous truth claims of the church, we don’t believe the church leaders have god in their ear. We don’t believe coffee to be any worse than Coke or Red Bull or any other diet soda that shall remain nameless.
Here’s a mormon coffee joke:
“Drinking a cup of coffee every day has great benefits”
“What are they?”
“For one, it keeps you from being Mormon!“
As you drink your first or your next cup of Joe, consider what it means to you.