Combine vinegar, salt, peppercorns, mustard seeds, and crushed red pepper in a small saucepan and heat over high heat, stirring, until the sugar dissolves – no need to boil. Remove from heat, add the cold water, and refrigerate until ready to use.
Divide the cucumbers, dill, garlic, and bay leaves between two clean 1-quart jars. Cover with the brine. Cover the jars and refrigerate for 24 hours.
The pickles will keep in the refrigerator for up to 4 weeks.