The proof is in experience: don’t drink coffee if you want a bigger dick.
I never drink coffee. I used to drink it whenever I hit the gym for some extra energy and pump, but even that wasn’t feeling right, so I stopped for months. The other day, I had a cup because it was late, I still had to hit the gym, and I was exhausted. The results were a tiny flaccid that lasted wayyy after the coffee wore off. I was getting worried because it lasted even after I had gone to bed and woken up. Only about 23-24 hours later did my turtle flaccid size get back to what is normally is (about 4 inches).
Stay away from it.