Something a friend who used to work for the telephone department used to do was swap the numbered buttons on the phone from left to right and right to left.
From this:-
123

456
789

to this:-
321

654
987

The few times he did it the people using the phone took ages to work out why they kept getting the wrong number.

ChrisTall
That really is my name!
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ChrisTall That really is my name!