thiru@9.2.0:SQL>revoke drop any table from thiru;

Revoke succeeded.

thiru@9.2.0:SQL>show user
USER is "THIRU"
thiru@9.2.0:SQL>drop table t;

Table dropped.

thiru@9.2.0:SQL>truncate table t2;

Table truncated.

-- Also when a GRANT ALL has been made on your table to a different user, that user will be able to truncate your table,irrespective of whether he has 'drop any table' privilege or not.

thiru@9.2.0:SQL>grant all on t2 to scott;

Grant succeeded.

thiru@9.2.0:SQL>connect scott/tiger;
Connected.
thiru@9.2.0:SQL>truncate table thiru.t2;

Table truncated.

thiru@9.2.0:SQL>connect thiru/*****
Connected.
thiru@9.2.0:SQL>revoke drop any table from scott;
revoke drop any table from scott
*
ERROR at line 1:
ORA-01952: system privileges not granted to 'SCOTT'

thiru@9.2.0:SQL>create or replace trigger drop_trigger
  2  Before drop or Truncate on Thiru.SCHEMA
  3  Begin
  4    Raise_Application_Error(num=>-20000,msg=>'Are you sure?');
  5  end;
  6  /

Trigger created.

thiru@9.2.0:SQL>show user
USER is "THIRU"
thiru@9.2.0:SQL>truncate table t2;
truncate table t2
               *
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-20000: Are you sure?
ORA-06512: at line 2

thiru@9.2.0:SQL>alter trigger drop_trigger disable;

Trigger altered.

thiru@9.2.0:SQL>truncate table t2;

Table truncated.