What is Mortal Sin?
The Council of Trent in Session 22 says: "...(1) those who are present shall have first shown, by their decently composed outward appearance, that they are there not in body only, but also in mind and devout affection of heart...They shall also banish from churches (2) all those kinds of music, in which, whether by the organ, or in the singing, there is mixed up any thing lascivious or impure; (3) as also all secular actions; (4) vain and therefore profane conversations, (5) all walking about, noise, and clamour, that so the house of God may be seen to be, and may be called, truly a house of prayer." Moreover, as written by St. Paul in 1 Tim. 2:9, "...(6) women also in decent apparel: adorning themselves with modesty and sobriety, not with plaited hair, or gold, or pearls, or costly attire..." It is uttmost blasphemy to show contempt for the mass and act in an unworthy manner, and especially towards the most holy Eucharist, the sacrifice of the mass, which is the sacrifice of Jesus Christ on the cross.
"And Jesus went into the temple of God, and cast out all them that sold and bought in the temple, and overthrew the tables of the money changers, and the chairs of them that sold doves: And he saith to them: It is written, My house shall be called the house of prayer; but you have made it a den of thieves (Gospel of St. Matthew 21:12-13)."