Anyway. I thought I'd share my secret with you today. It's really one of the easiest tricks in the baking book. Master this one, and you, too, can frost cupcakes like a professional! (Really, though - if you haven't tried this, you should!)
Once you've made your frosting (use whatever buttercream recipe you like, but make sure it's good and thick), get a large Ziplock baggie and set it up in a cup (I used a 2-cup measuring cup because I'd made a large batch of frosting; could also use a coffee cup or whatever). Make sure one corner of the bag is down in the cup so that most of Fill the baggie with frosting. I usually stick the whole cup in the fridge for a bit at this point, because it can be a little warm from all the mixing and moving. Good to let it chill for a few minutes.
Once chilled, take the bag out of the cup, smoosh all the frosting into the corner as best you can, and then gather the top of the baggie like a standard pastry bag. Use scissors to cut the corner off the Baggie - make a pretty good sized cut, so that you get a nice flow of frosting. (Hint: It's generally better to make a small cut and see how much frosting comes out, then cut more as necessary.)