What the deal with honorary Military Titles?

Over the years, in the news, and in books, I’ve read about American people getting honorary military ranks: Colonel so and so for example. Are those ranks earned, or conferred by some organisation, or can people just call themselves by that rank?

As an UK doper, can I call myself Colonel or whatever?

Perhaps this link to the Honorable Order Of The Kentucky Colonels will help.

But, more simply, the US Constitution forbids citizens from using titles of nobility, & this is the next best thing.

Didn’t President Nixon make Elvis Presley an honorary Drug Enforcement agent?

Yes, Pres. Nixon was obviously looking for someone with expertise in the area. IIRC Elvis actually took a gun with him to the white house to present to the trickster.

Homer Simpson, episode 8F19 Colonel Homer