You disappointed me. Notice that is meant ironically. If you really are disappointed you would say it differently. e.g. * Ik loop de marathon in 2.30. - Dat valt mij van je tegen --> That disappoints me. (ironically) - Je tijd valt tegen --> Your time is disappointing (seriously) - Je stelt mij teleur --> You disappoint me.

Dat valt me van je tegen. - This dissapoints me of you.