You need to do some fact checking before you tell someone they need a lesson. The U.S. agreed to ICJ decisions since we created the U.N. and its charter, which includes the ICJ statute. This is therefore a case of compliance with our agreements and, by extension, with our Constitution. Just because you don't like it, doesn't make it unconstitutional.
If the President agreed to a treaty suspending habeus corpus and the Senate signed on, would that be binding? How about a treaty abolishing the Constitution?
There have to be Constitutional limits to the scope of the treaty provision, otherwise the provision itself and the Constitution are meaningless.