The most obvious is that most girls won't find being the victim of a wedgie that amusing.
Do you think I should continue to kill you asses? If you use something like tape or a stick that is just short enough to have the sleeves hang over the ends, this can be an incredibly hard wedgie to get out of next to a hanging wedgie or hogtied wedgie.
So I kept an eye on him.
All you have to do is find a way to distract your victim long enough for you to pull up said victim's underwear as high as you can, causing an unpleasant sensation in the crotch and between-the-cheeks region.
You can just sneak up on your victim and reach for your victim's underwear, or you can casually approach your victim as if you just wanted to say hi or chat about something, and then trick your victim into turning around.
If you are working with someone else, let them pull up on their end.