Coffee makes my penis shrivel when the caffeine gets into my bloodstream, it also gives me cold feet which shows that circulation is reduced to the body’s extremities.
Caffeine raises your blood pressure due to vasoconstriction and your heart working harder to pump the same amount of blood around the body, this eventually causes your heart to fatigue and when the caffeine effects wear off (around 4 hours after consumption) you end up with a lower than normal blood pressure which makes you drowsy. I believe that this effect can also reduce erection quality so it is best avoided before or after PE.
Once, several hours after drinking lots of Coke, I had difficulties getting a full erection.
I find the best things to consume before PE are known vasodilators like, ginger, ginseng, spicy food, 1 glass of alcohol, etc.