The two worst short tongue twisters I know are :-
Peggy Babcock
and
Rubber Buggy Bumpers

neither of which can really be said twice in a row without practicing.

in song, the only one which springs to mind is the chorus of Mary Mack's Mother:-

   Mary Mack's mither's makin' Mary Mack marry me
   My mither's makin' me marry Mary Mack
   When I marry Mary Mack, Mary will tak' care of me
   We'll a' be makin' merry when I marry Mary Mack

jim