Place asparagus spears tips-down in a 1-quart lidded jar. Add garlic, peppercorns, dill and crushed red pepper, if using.Advertisement
Combine vinegar, water, sugar and salt in a small saucepan; bring to a boil over medium-high heat. Boil, stirring occasionally, until the sugar is dissolved, about 3 minutes. Remove from heat.
Carefully pour the vinegar mixture over the asparagus mixture in the jar; screw the lid on tightly. Immediately place in the refrigerator. Chill for at least 8 hours.
To make ahead: Refrigerate in a sealed jar for up to 2 weeks.