PORTABLE-CONDITION-SYSTEM> (flet ((my-report (condition stream) 
                                    (declare (ignore condition))
                                    (write-string "asdfsfgsa" stream)))
                             (define-condition foo-condition () () 
                               (:report my-report)))
FOO-CONDITION

PORTABLE-CONDITION-SYSTEM> (princ (make-condition 'foo-condition))
asdfsfgsa
#<FOO-CONDITION {1008CC87C3}>