Slightly less informally, we have:
イベントを立てちゃってね。
The 立てちゃって of course comes from 立てちゃう, a spoken version of 立ててしまう, so I'm guessing the な in 立てちゃいな is what's confusing. Unlike the prohibition な, which attaches to the dictionary form of the verb (するな, 食べるな), this な attaches to the ます stem to form an informal command. It's friendlier than the blunt しろ-type of command (食べろ, 行け, etc), but it's only appropriate for informal situations (which is why I substituted with the ~てね command form). You often find it with the emphatic よ tacked onto the end. Some more examples:
早く行きなよ(≈行きなさい/行ってね)。 Hurry up and go!
旅行を楽しみなよ(≈楽しんでね)。 Enjoy your trip, OK?
しおり、文句を言わないでご飯をさっさと食べなよ(≈食べなさい)。 Shiori, stop complaining and finish your food!
I seem to recall reading somewhere that this is primarily a feminine expression, but I can't locate that particular statement at the moment, so I'll wait for someone else to clarify that.
なhere is actually not an imperative/command. It means suggestion. I.e., 'I suggest you leave shortly', 'I suggest you enjoy your trip', etc. That is why it is milder. Your equation行きなよ=行きなさいis not accurate.なis not feminine at all, butねis feminine (sometimes). – Jul 08 '11 at 13:18