Short and Sweet:
* Four forks for four folks.
* Fork the fork, it's too far.
A Bit More Challenging:
* The fork was forked and frayed, but Fred fixed the fork with a file.
* Peter Piper picked a peck of pickled peppers. If Peter Piper picked a peck of pickled peppers, where's the peck of pickled peppers Peter Piper picked? (This one uses "p" sounds, but incorporates the "f" sound of "fork".)
Silly and Fun:
* Fuzzy Wuzzy was a bear. Fuzzy Wuzzy had no hair. Fuzzy Wuzzy wasn't fuzzy, was he? (This one uses the "f" sound and is silly, but it's not specifically about a fork.)
You can also create your own tongue twister by using words that start with the "f" sound and the word "fork." Have fun with it!