In a small saucepan, combine the beer, vinegar, sugar, salt, peppercorns and red pepper flakes. While stirring, bring to a simmer over medium-high heat and cook just until the sugar and salt dissolve, about 3 minutes. Remove the brine from the heat and let it cool to room temperature.
Pack the cucumbers into an airtight container. Add the dill. Pour the cooled brine over the cucumbers, making sure everything is submerged.
Cover and refrigerate for at least 24 hours before serving. Store in the refrigerator as is for up to 1 week, or use proper canning techniques for shelf storage.