1/4tspcrushed red pepper flakes, add a little more if you like things spicy
salt, to taste
Slice the cucumber lengthwise and chop into 1/4" slices. Put the cucumber in a bowl and toss with the vinegar, garlic, cilantro, and red pepper flakes. Add salt to taste. Refrigerate until ready to serve.
For best flavor, refrigerate for at least an hour before serving.