Pudding Brain is the state that one gets into around Christmas time in the office. This implies that you are preparing for Christmas holidays and in no state to complete any actual work.
Pudding Brain can carry over at any time of year and can be used when you are in no frame of mind to be useful within your place of employment, usually on a Friday afternoon.
For example, "today I have pudding brain" which essentially translates to "I won't be doing anything helpful today because I am lazy."
Used for when you wanna tell somebody they said some stupid thing in an argument.
Shut up you’re literally a pudding brain, don’t say some dumb shit like that again.