A hangover - the terrible feeling you have, headache, body pains, bad taste in your mouth, after waking up the morning after being drunk Mother of all - this is a metaphor. Mothers give birth to children and are thus the originator of life. The mother of all something means the originator of that thing, the biggest, most original. So the mother of all hangovers is the biggest, and worst, hangover ever!

This is a language structure bestowed upon us by Saddam Hussein, who promised those military forces opposing Iraq's seizure of Kuwait the "mother of all battles". The phrase is now used to describe a noun in some great sense. The "mother of all hangovers" must be a terrible experience, the greatest hangover of all time.

that means a mum who got drunk!