Concerning the bow during the incarnation:
The GIRM (n. 298) reminds us of the ancient tradition of seeing the altar as representing Christ, the Living Stone (cf. 1 Peter 2:4). Because of this association, a bow of the body is prescribed as the normal gesture made toward the altar, as if toward Christ himself. In particular, all the ministers bow toward the altar when they arrive at the sanctuary at the beginning of Mass and at the end of Mass, before leaving the sanctuary. The priest or deacon also bows during other moments during the Mass, for example, when preparing to proclaim the gospel. In addition, this “profound bow” is made by the entire assembly during the Creed at the words "by the power of the Holy Spirit . . . became man."
Concerning the kneeling during the Liturgy of the Eucharist:
(GIRM no. 21): a. The people stand while the presidential prayers are being said, therefore, during the prayer over the gifts. b. Thy also stand throughout the eucharistic prayer, except the consecration. The practice is for the faithful to remain kneeling from the epiclesis before the consecration until the memorial acclamation after it. c. The people may sit during the silence after communion.
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**In the dioceses of the United States of America, they should kneel beginning after the singing or recitation of the Sanctus until after the Amen of the Eucharistic Prayer, except when prevented on occasion by reasons of health, lack of space, the large number of people present, or some other good reason. Those who do not kneel ought to make a profound bow when the priest genuflects after the consecration. **The faithful kneel after the *Agnus Dei ***unless the Diocesan Bishop determines otherwise.
**As far as dress during Mass, I won’t condemn anyone, however I will not be approaching the Altar of God and God himself in my gym clothes anytime soon. On a side note, I am of the opinion that many (but not all) girls (high school and college aged) come to Mass wearing clothing that scandalize people around them. I am sure you may think that people should not be looking and scandalizing themselves but I believe both the scandalizor and the scandalizee are equally of guilt. Its not a new revalation to realize that men are more visually vunerable to sin, afterall, is this not what modern advertising has proven time and again?