I don't think so. The domain's administrative and technical contact is one 'Selino Valdes', which has a website at http://selino.com/, which seems pretty serious. flojuggler.com has existed since december 4th 2009.

On his site, Selino showcases Flojuggler as

  The premiere menstrual tracking application. Designed to
  track the cycles of multiple persons. The focus of the
  service is not medical but more lifestyle.

It could be an elaborate joke that has me fooled, but actually: why would this be a joke? I admit that I don't have a clue why I would want to track anyones period, but perhaps there really is an audience, in which case the courage to go through with such an awkward subject could net him quite a few $.

The signup page is interesting from a privacy-backlash perspective. Two of the bullet points are:

  * Can I easily delete my info?
    Hells yeah! This is your data, your pictures, etc. At
    any point just hit the delete button and it's gone.
    There's no waiting for approval. This ain't Facebook or
    Yelp.
  * Why not use Facebook Connect?
    Seriously? Do you even want a chance that Facebook is
    gonna announce that you use Flojuggler?

That also makes is seem like some thought went into it.

As to the 'why?', another bullet point clarifies:

  * Why do I need to know when my girl/girls are bleeding?
    Hey, if you like a little rainbow kiss in your diet 
    then that's on you. We don't judge. Personally we prefer 
    hitting the skins when the lake isn't muddy. Sometimes
    ladies have really bad PMS, too. It's a good thing to
    know BEFORE you get home.

I think it's a shame to perpetuate/encourage the idea that there is something inherently dirty about menstruation and I think many 'PMS' claims are just easy ways to excuse/blame bad behavior on some days, but: there's your audience.

Aside: anyone care to explain the 'rainbow kiss' idiom to a non-native English speaker?

I'm really not sure.