RSRH Zatzal says that: מִסְתּוֹלֵל means to imagine yourself being immensely higher than others. The Mitzri held himself way above Klal Yisroel. Why after Makkas Sh'chin is the Middas HaGa'ava of the Mitzri addressed? RSRH Zatzal says that Sh'chin means an inflammation rash. The skin of the Mitzri'im had been inflamed into hot boils. Why hot boils? The Baal Ga'ava blows himself up. Also, Sh'chin is a form of Tzora'as, and one of the causes for Tzora'as is Ga'ava. (Gemara).
This: עוֹדְךָ מִסְתּוֹלֵל was a warning. After the message of Sh'chin, you are still a big shot? Here comes Barad! Rabbi Akiva Eiger explains why the Barad smashed only the:
פִשְתָּה וּשְׂעוֹרָה flax and barley, since they were standing like Baalei Ga'ava (in their stalks), unlike the: חִטָּה וְכֻסֶּמֶת wheat and spelt, which “laid low” since they weren’t ripe; this was again a lesson against Ga'ava.
And right after Makkas Barad it says: עַד מָתַי מֵאַנְתָּ לֵעָנוֹת מִפָּנַי “How long will you stubbornly refuse to have Hachna'a and Anava before Me?” (Rashi). Both Sh'chin and Barad were severe punishments for Ga'ava. The same Lashon of: מִסְתּוֹלֵל (Ga'ava) is used by Yosef HaTzaddik, who was: מְסַלְסֵל בְּשַׂעֲרוֹ (he played with his hair), and לְסִסוּל means Ga'ava (as Chazal say: נִהַּקִים נָהֲגוּ לְסִסוּל בֶּן מָצְעַירושלמי בכורים א ה the Cohanim conducted themselves on a higher level). Yosef knew how to use Ga'ava in a positive way, and when he told the wife of Potiphar: אֵינֶנוּ גָדוֹל בַבַּיִת הַזֶּה מִמֶּנִּי “I am the greatest person around here”, he saved himself from Chet.
