My butt is pretty large too.  I barely can wear jeans (regular cut) in my waist size.  The relaxed fit is the way to go.  I also wear micro fiber briefs (WalMart has a good selection.  I find these let the jeans "slide" over my butt.  I have found cotton briefs get pulled down if I do a lot of bending over and have to be "adjusted" in the rest room.
      
      
    10 years