Subclause 9.3.4.6 [dcl.fct] paragraph 6 specifies

A member-declarator with an explicit-object-parameter-declaration shall not include a ref-qualifier or a cv-qualifier-seq and shall not be declared static or virtual.

This does not address the situation when an explicit object member function becomes implicitly virtual by overriding an implicit object member function. That should be prevented.

This also does not address class-specific allocation and deallocation functions, which are implicitly static.