Dictionary Definition - Spoonerism - A transposition of sounds of two or more words, especially a ludicrous one, such as Let me sew you to your sheet for Let me show you to your seat.
History - Named after William Archibald Spooner (1844-1930), British cleric and scholar. His most famous utterance "the lord is a shoving leopard"
I have faith that the CC community can provide a few lovely modern day examples of this rarely acknowledged delightfully amusing involuntary verbal tic.
I'll start the roll bolling
Please excuse the vulgarity of my current favorite spoonerism I have chosen to share with you.
"I haven't had a .... all night drinkstable" rather rude, and won one of my friends a sleep over at the local police station.