What inmates in jail shout out to other inmates to alert them that a corrections officer (c.o) is walking around close by checking for contraband or illicit activities.
Joker hid the stash when he heard someone yell out "man walking".
An elder person who is 90% right in regards to historical accuracy and the present status of earthly things. Although 99% wrong when it comes to future events (including but not limited to) the fact they are still alive after having foreseen themselves dead for years.
Bob: “Old Higgins said that the economy is doomed to collapse next month…”
Ron: “Well you know he’s got old man walking. Poor guy…. He was just diagnosed a couple months ago.