I have heard of people on non cake forums talking about buttercream flavors like kiwi strawberry and stuff like that.

How could I do this

I am a cupcake baker but I make all sorts of flavors of buttercream. I basically use IndyDeb's recipe. For a lot of the flavors I just replace the liquid with another liquid like coffee, coffee creamers, juices, etc. I also just add pureed fruit, peanut butter, etc to the frosting and adjust the other ingredients to get the right texture.

HomemadeUpgrade,
When you use different liquids to flavor it, does this icing still crust? Sounds yummy!

Most of them do still crust, yes. The only one I've had trouble getting to crust well after altering is adding pureed strawberries. It still holds up well on my cupcakes but if you're looking to use it under fondant on a cake it might not be what you're looking for. All of my other flavors crust up just fine.