What is "Yabi'u"?
Radak: This is speech. The same applies to "Tabanah Sefasai Tehilah" (119:171). "Yedabru" repeats the matter to strengthen it. They constantly speak haughtily over us.
Malbim: So they say [haughtily, and claim to prove that Hashem does not oversee the world].
What is "Asak"?
Radak: It is a haughty, strong matter.
What is the meaning of "Yis'amru"?
Rashi: They brag. This is like "He'emarta" and "He'emircha" 1 (Devarim 26:17-18).
Radak: They are proud and aggrandize themselves over us. The same applies to "Es Hashem He'emarta" (Devarim 26:17) - you aggrandized Him.
Malbim: Refer to 94:4:1:2.
Rashi (Devarim 26:17): In both places, it is an expression of separation. (There it means that you designated Hashem from all gods to be Elokim to You, and He designated you to be His nation. Here, the reflexive conjugation means that they separate themselves; they consider themselves superior. - PF)