Raw cucumbers are often bitter tasting, particularly on the darker end. Here is a sure "cure" for that! When I first heard about this, I was skeptical, but I assure you, this really works.
Here is a washed cucumber:
First, cut a piece off of the dark end:
Next, rub that piece around and around for several moments on the place it was cut off from. You will notice a milky exudate forming under the skin of the cut surface. After a few moments, discard the little cut off end and wash the white substance off under cold running water.
Now, your cucumber is ready to eat! No bitterness!