I should specify that these are mostly more couple-y/family oriented holidays. There is nothing specific you can do to creep people out as a single person on St. Patrick's Day or Halloween because those days are essentially built for single people to be creepy.
New Year's: When the clock is about to strike midnight, position yourself close to a couple that are strangers to you. As they start to engage in the traditional New Year's kiss, say/do one of the following:
A) Slow clap.
B) "Aw yeah!"
C) Save by the Bell "OooOOOoOooOOo" audience noise.
Valentine's Day: Buy yourself a heart shaped pizza for delivery. In the special instructions, ask for a pizza for one and instruct the delivery person to tell you how beautiful you look. Make sure to say that the tip will be increased if the delivery person can say it with sincerity and enthusiasm.
4th of July: Grab some champagne, or sparkling juice, chocolate covered strawberries, a blanket, and a giant teddy bear (or body pillow). Head to your nearby park/beach (wherever they shoot off the fireworks). Set everything up and cuddle the crap out of your "girl/boyfriend" as the fireworks go off. Creep factor only works if you are near large groups of people.
Thanksgiving: Put your dining room table next to the biggest window in your home. Set the table as fancy as can be. Open the curtains for the world to see. Buy yourself a turkey sub and eat that sucker at your table. Don't bother using any of the place settings and stare out the window all forlorn like.
Christmas: Gather your prized collection you have laying around the house. I, for example, have a Brewer Bobble head collection. Grab a camera, set it up to take a selfie, position yourself in the middle of your collection. BAM! Christmas Card that says "From my family to yours."
My New Year's resolution is to do all of these items for 2013.
