Try Nike Pro Combat compression shorts and use 2toms Sports Shield + Aquaphor instead of vaseline.  Desitin is also much better than vaseline.  I usually apply the Sports Shield  before the start and then apply Aquaphor or Desitin to hot spots as needed.  Sports Shield comes as a roll-on which is very handy for the cracks and other delicate places.  The best compression shorts I ever had were Pearl Izumi compression shorts (Laser???) --  a few models before their current Infinity Compression (haven't tried) but I lost them while changing shortly after I finished a 100 miler.  The Nike shorts are really underwear, whereas the old Pearls were like bike shorts without the padding.  I also have never had a problem with my CW-X tights but haven't had the occasion to wear them for an ultra in a very long time.

I have never tried this, BUT, I always use nickel-sized moleskin cutouts for my nipples, and it seems like a similar approach would provide excellent protection for sack skin; however, removal might be a problem. 

I wear shorts that I've ripped the liner out of.  Not chaffing, just hanging clear and easy.  Of course I'm really skinny so my thighs don't rub.

I use Skins A200 and have run 2 x 100 milers and numerous long runs in them and have had no problems at all, I call them my "budgie smugglers" as it provides a lot of support around my ball sack. Yes they are quite expensive but I have found them brilliant, cool in the sun, warm in the winter, be it a Britisih winter.

I use Asics 2-N-1 shorts, with built-in compression liners. I chafe badly with regular shorts, generally no problem with these. For 100 milers, there is still some chafing.

I've seen this recommened a couple of times now.

 

There are 3 types of desitin.  Cream, Paste and ointment.  Which type is being recommended?

Ointment (Desitin or Aquaphor).  Aquaphor comes in a pocket-sized 0.35 oz tube; I can't say that I have seen anything nearly that small with Desitin.  Desitin is one I reserve for a drop-bag, because of its size and difficulty with removal.  I have a preference for Aquaphor, but like most things mentioned here, just keep trying stuff until you find something that works, as these are highly individualized issues.

Just wondering, but in a pinch (no pun intended), when chaffing has gotten bad,  has anyone here just cut out the briefs all together, smeared up with your favorite anti-chaff cream, and just run with the outside part of the shorts?  Just let the boys swing so to speak so?  Just wondering if this made it better or worse, really.