Make the dressing: In a small pan, heat the honey over medium heat until it froths and turns golden brown, 2 to 3 minutes. Remove from heat and carefully pour the vinegar over it. Return to heat and simmer to reduce for a minute. In a bowl, whisk together the sesame oil, soy sauce, and red pepper flakes. Season with a pinch of salt. Whisk in the honey mixture.
Prepare an ice bath: Fill a large bowl halfway with ice cubes and add some cold water. Place a colander squarely inside the ice bath. The colander will keep you from having to pick the asparagus out from amongst the ice cubes in the ice bath.
Add salt until the boiling water tastes like seawater. Add the asparagus to the boiling water and cook for 1 1/2 to 2 minutes - you want them to be crunchy. If the asparagus are thin, cook for only 1 minute. Remove the asparagus from the water with a strainer and transfer them to the colander inside the ice bath. Allow them to cool completely for a few minutes and then place them on a kitchen towel to drain any excess moisture.
Toss the asparagus, sesame seeds, and the sauce together and refrigerate for 1 hour, or until ready to serve.