Not actually a joke per se, but I thought the retired core membership (aka "the old and bold") might appreciate the end of a telephone conversation overheard recently. 
We came into the room just as an acquaintance of ours, Peter, a retired 2-star civil servant latterly of the Ministry of Justice, was concluding a telephone call with some jobsworth, I believe in the local council planning department, who was clearly trying to put the standard set of obstacles in the way of what Peter wanted to achieve in the hope that he would just go away and stop causing him work.
Peter's parting shot:  "Now that I am retired, you won't believe how much time, energy and experience I have to make your life a misery"....... phone down!
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.....Okay - proper joke:-
Psychiatrist to Selection Board Officer (SBO) at the OASC - "How do you decide how to stream applicants to be either Fighter Controllers, Air Traffic Controllers or Flight Operations Officers?"
SBO: "We fill a bathtub with water and give the applicant a spoon, a cup and a bucket and tell them to empty the bath.
Psychiatrist:  "Ah! so the ones who use the bucket go Fighter Control?"
SBO:  "No, they go Air Traffic and the ones that use the cup go Flight Ops"
Psychiatrist:  "So how do you pick the Fighter Controllers?"
SBO:  "We take the ones that pull out the bathplug"
Psychiatrist:  "What about the ones that use the spoon?"
SBO:  "We tell them to re-apply after 1st April as the RAF is creating a new Branch for which they seem admirably suited".