Adj. Immature in the ways young men are immature. A lad (or laddie) magazine is a publication, such as Maxim, nicely described on urbandictionary.com as “catering to oversexed braindead morons and featuring double-extra-soft porn (no actual nudity), gadgets, sports, cars and beer.” Google Ngram. Girls may find this band icky, and parents may wish it had some manners, but Blink 182 showers its fans with laddish love. (Ann Powers, New York Times, June 18, 1999)/And shame on us, really, for not being more on top of our buzz and getting the inside track on James Blake, but The Vaccines were really great – in a laddish, London’s Strokes kind of way – even if they did only play four songs. Hartford Advocate, March 17, 2011)
notoneoffbritishisms.com 
An even more recent example, from yesterday’s NY Times story about the cable channel Spike getting rid of its slogan (“Get Some Action”):
>>The slogan is disappearing from Spike’s promotions and advertising, executives say, along with the more overt expressions of the so-called laddish behavior that the channel has celebrated.<<
That quote actually inspired the post. Interesting that the writer used the qualifier “so-called,” indicating that the word isn’t yet fully absorbed into Amer-English.
Note the use also of “missish” by Austen in P & P, in the book and in the BBC miniseries. Jane’s father asks her not to be too “missish” which I suppose means “overly prim.”
It’s strange how some Britishisms seem to undergo subtle alteration in the course of their journey west. Have never, for instance, heard of a “laddie magazine” over here in GB. “Laddie”, quite apart from the fact that it sounds shortbread-and-tartan Scottish, comes across as distinctly old-fashioned and not a little twee: not at all what you’d associate with laddishness! And it’s not “lad magazines” either (those, if they existed, would be about and not for lads): the term is “lads’ mags”.
Ben, have “ladettes” yet reached North America? They go in for more or less all the same moronic activities as their male counterparts, but with even more indecorousness as they totter (and often collapse) into the gutters of so many British town centres at pub and club chucking-out time on Friday and Saturday nights.