You can indeed issue fake currencies. The only technical limitation is that currencies are (as it stands) limited to 3 letters.
Note that your friend would only be able to trade your fake currency to someone who is willing to trust you, so there's no obvious need to have more technical enforcement preventing trades.
Well, the main design is that people will use this for real-world currencies. If people are interested in starting to issue fake ones with arbitrary names, it's probably worth raising with the developers! They're hanging around in #stellar-dev, and I'm sure would love feedback :).
Note that your friend would only be able to trade your fake currency to someone who is willing to trust you, so there's no obvious need to have more technical enforcement preventing trades.