Heat the vinegar in a small saucepan over low heat until just warm. Keep an eye out so that it doesn't boil; you want the warmth of the vinegar to seduce the coy, subtle flavor out of the blossoms, not immolate them.
Meanwhile, plunge the flowers in a bowl of cold water and gentle swish them around to flush out any dirt and bugs that have taken up residence. Dump the flowers into a colander and thwack it against the side of the sink to shake off the excess water.
Stuff the pint jar with the blooms. Don't be too Martha about this. It's okay if the blossoms get crushed a bit.
Pour enough of the warm vinegar into the jar just to submerge the blossoms, using a metal spoon to push down any errant blooms that want to float up over the top. You might not need all of the vinegar.
Let the vinegar cool, then place a square of parchment paper over the opening of the jar and screw on the top. You want to make sure the vinegar doesn't come in contact with the metal lid, as the acid will erode the finish of the cap and do nasty things to the taste of your infused vinegar. Of course, you can make short work of this by using a glass-lidded canning jar--I just can never find them. Place the container in a dark, cool spot that's so hidden you'll forget about it. This infusion benefits from a long steep--1 to 2 weeks minimum. Trust me, the vinegar will bless you abundantly for your patience--or your forgetfulness.
When you're happy with the chive-y strength of the brew, strain it through a fine sieve and toss the spent blossoms. Pour the vinegar into your favorite (preferably glass) sterilized bottle with a rubber stopper and display prominently. Its hue--the blush of a very embarrassed Rosé--is a great conversation starter. Just don't forget to use it.