Spoonerism
A spoonerism is an error in speech in which corresponding consonants, vowels, or morphemes are switched (see Metathesis) between two words in a phrase. These are named after the Oxford don and ordained minister William Archibald Spooner, who was famous for doing this.
An example is saying "The Lord is a shoving leopard" instead of "The Lord is a loving shepherd." While spoonerisms are commonly heard as slips of the tongue, and getting one's words in a tangle, they can also be used intentionally as a play on words.