This was Death's alias, assumed when he enlisted in the Klatchian Foreign Legion to try and forget, shortly after the deaths of Mort and Ysabell. Whilst there, the fort he was in was attacked by D'regs. As all the men were being slaughtered by the volleys of arrows, Beau Nidle had the nifty wheeze of propping up the dead to make the enemy think they are still outnumbered. This would have been great had it not been done so often before. However, this time, when the D'regs attacked, the corpses, Nudger Malik included, fired back! Once the D'regs were routed, the corpses then dug their own graves.
This gave the sergeant even greater impetus to try to forget than he had when he first arrived.
Based on the Beau Geste adventure stories written by P.C. Wren, but Pratchettised to become a pune on "Bone Idle", as in tremendously lazy (and with the emphasis very much on bone). For very British wit, see also the fantastic comic strip Beau Peep, another play on the Beau name, this time parodying the nursery rhyme character Bo Peep.