Rashi on Exodus 10:2/רש"י על שמות י׳:ב׳

1התעללתי means I HAVE MOCKED, as in, (Numbers 22:29) “Because thou hast mocked (התעללת) me”; (I Samuel 6:6) “Indeed, when he mocked (התעולל) them”, which, also, is said in reference to Egypt. It is not an expression denoting doing and action, for were this so it should have written עוללתי, similar to (Lamentations 1:22) “And do (עולל) unto them as thou hast done (עוללת) unto me”, and to (Lamentations 1:12) “which he has done (עולל) unto me”.