36th President: Lyndon B Johnson, 1963
Mash = 36 (Johnson was the 36th president)
John's son = Johnson
NOTE: The John is another name for a toilet.
Pyjama = 963 = 1963 became president
Leaned on = Lyndon
His dad ate mash (36) as he sat on the john, while the john's son (Johnson) was used by the pyjama boy (963 = 1963).
Connect Johnson to Lyndon
Sometimes the john's son (Johnson) just has to be leaned on (Lyndon) when you're not feeling well.
NOTE: The way Mammoth Memory remembers Lyndon is to think Lyndon – leaned on.