The phrase "as a joke when" is correct and usable in written English.
It can be used to indicate that something was said or done humorously at a specific time or in a particular context.
Example: "He made that comment as a joke when we were all laughing about the situation."
Alternatives: "as a jest when" or "in a humorous way when".
Abra makes a drunken proposal to her in episode "Bad Reputation" however laughs it off as a joke when she assumes he is not serious.
Syria's political opposition denounced the law as a joke when it was announced last month.
His services are often called upon as a joke when the conversation gets boisterous.
"It started as a joke when I was with my partner because I was spending a lot of time with them.
"Why was Truman seen as a joke when he left office and now he's in the top 10?" Mr. Osborn said.
I think I said it to him once as a joke when he was about to turn 40, and it's obviously hit a nerve with him.
One man has his arm around the neck of his friend and a smile on his face as if they had been cracking a joke when death overwhelmed them.
Jessica Thom, the other Touretteshero co-founder, has previously written in the Guardian in 2012 about Tourette syndrome being used as a "cheap joke" when it was used by David Cameron in an interview.
"We chose it as a bad joke when we first started," they admit.
There are many people who are caring, sensitive individuals who do not view the use of "retard" as disrespectful or heartless, particularly when used as a joke or when not referring to someone who actually has a disability.
He likes them so much, he started the Cloud Appreciation Society (initially as a joke - when asked to give a lecture on clouds at the wonderful Port Eliot lit fest, he was worried nobody would turn up and so he made little cloud badges to give out and billed it as the society's inaugural meeting), which now has 3,900 members in over 39 countries.
