Best I know this is a fairly recent slang word coined in the past 10 years or so, because I don't recall it being around when I left Germany in 1993. There are whole lists of humorous word creations along the lines of "Warmduscher", e.g. the one above

AFAIK the word was formed by the late-night-talker "Harald Schmidt" in one of his shows.

Not all of the followups were made by Harald Schmidt and his ghostwriters. Instead many were formed by everyday people (german boulevard paper "BILD" even made a contest on this topic IIRC).

Due to the specifics of german language those words are difficult (if at all) to translate into other languages.

Norbert: Thanks for the link - it's great! :D

Nicht nur die Bildzeitung - sogar der Spiegel fand die Wörter so erwähnenswert, dass er ihnen einen Artikel widmete. War also ein 'ernstzunehmender' Sprachtrend. Habe ich aber schon ewig nichts mehr drüber gehört.
Warmduscher sind Weicheier, die nicht hart genug sind, die Dusche auf kalt zu stellen, Kaltduscher sind cool. :-)