In the Denver Post of 15 Apr 1919, a list was published of young men who had registered with the local draft board but failed to appear when called. Versions of his list had been published already, and the Post devotes some large print and column inches to asking for corrections, noting that some of the men listed as "army slackers" may have enlisted already and even died at the front, but by failing to notify the draft board, well, paperwork.
I stumbled across this because William Nelson Plantz appears on it. I believe at the time he was building radio towers for the Navy in France; that's where he met and married his wife. Probably not a "slacker".