The entire Psalms, Tanach and the Siddur (the Jewish Prayerbook) is replete with the demands of people to G-d to grant us our requests and to bring the Redemption, as in the Biblical expression: "Ad Mosai!"1
Abraham demanded of G-d to spare the wicked people of Sodom.4 Moses complained to G-d when things got worse for the Jews in Egypt.5 The Jews were deemed correct when they demanded an opportunity to bring the Paschal offering which had been denied them.6
From all of the above, it is clear that G-d wants our demands,7 and that they are not a sign of disrespect, but rather a sign that we care for Him and His people.
Obviously, if we would tell G-d, either give us what we want or else we will abandon you, G-d forbid, that would be wrong. Our demanding Moshiach expresses the very opposite sentiment. It means that we realize that it is G-d, more than anyone, who wants us to leave Galut and to bring about the Redemption.
G-d is the one who asks of us to be able to fulfill the Mitzvos "in accordance with His will",8 something we cannot achieve in Galut because we don't have The Holy Temple. To want and demand Moshiach, is to want, more than anything else in the world, to be able to comply, with G-d's Will.9
If you don't like the word "demand," don't demand, but ask, beg, implore, beseech, cry, wail, pray. Our problem is not that we're too overbearing with G-d when it comes to Moshiach, but that we put too little emphasis on our requests for Redemption. We've resigned ourselves to Go/us and our prayers for Geulah are often said, in a perfunctory manner.
1. For example: Zecharya 1:12; Tehillim 6:4, 74:10, 90:13; Daniel 12:6; Tikkun Chatzos Prayer. See Hisva'adiyos 5744, vol. II, p. 986ff.
2 . Beis Yosef on Tur-Orach Chayim 188.
3. Commentary on Siddur, sec. 168.
4. B'reishis 18:23ff.
5. Shemos 5:22-23
6. Rashi, Baimdbar 9:7.
7. See Rashi Shemos 32:10.
8. Mussaf Prayer of Shabbos.
9 . See Schochet, Mashiach, p. 61-64 for additional sources for the requirement of a Jew to demand Moshiach.