Why are Madeline McCann and a submarine the same? They are both under the sea and full of semen.
Why are you making a sexual joke about a missing child? Thats awful.
you can't expect a grown up man to not think about sex now and there.
Jokes about a child victim is not funny nor is it appropriate. Losing a child is a very painful and traumatic experience to go through. Even over time the family will still continue to be affected and you should take this into consideration before joking about their lost family member.
You shouldn't be controlling people's thoughts.
Your thoughts are your own to have, however making crass jokes about victims publicly doesn't protect you from scrutiny. Tasteless jokes such as these only bring up harmful memories for the victim's friends and family.