The Catholic priesthood is disproved in 1 Timothy 4:3, where Paul warns Timothy that in the last days apostates in the Church would forbid marriage. Catholic priests, contrary to the Bible, are forbidden to marry. In view of this verse, and since we're living in the last days, how can you possibly defend your priesthood?
First of all, how do you know we're in the last days? Your question implies that because Catholic priests don't marry these must be the last days--not a good argument. Perhaps you're unaware that for the last 850 years (since the Second Lateran Council in 1139), all candidates for priestly ordination in the Roman rite have been required to take the vow of celibacy. By your reasoning that means we've been in the last days an awfully long time.
There's another problem with your assertion. No Catholic is forbidden to marry. Men who become priests do so voluntarily with the understanding that in the Roman rite marriage is not an option for priests.
Rather than being forbidden to marry, Catholic priests freely sacrifice the option of marriage in favor of serving God more single-mindedly as chaste, celibate disciples. (Married men in the Eastern rites of the Catholic Church are allowed to be ordained.)
Although marriage is lawful for all Christians, it's not mandatory. It's in harmony with the Gospel to abstain from marriage for the sake of serving Christ. Jesus tells us that some "have renounced marriage for the sake of the kingdom. Whoever can accept this [a life of celibacy] ought to accept it" (Mt 19:12).
Paul, himself a celibate priest, explains in 1 Corinthians 6:12-13 that "everything is lawful for me, but not everything is beneficial. Everything is lawful for me but I will not let myself be dominated by anything." Here Paul warns against sexual immorality and exhorts Christians to "glorify God in their bodies" (1 Cor 6:20).
In the next chapter he encourages celibacy by explaining its eminent role in a life of chastity:
Now, in regard to the matters about which you wrote, it is a good thing for a man not to touch a woman, but because of cases of immorality every man should have his own wife and every woman her own husband. . .
Indeed, I wish everyone to be as I am [celibate], but each has a particular gift from God, one of one kind and one of another...Now to the unmarried and to widows I say, it is a good thing for them to remain as they are, as I do, but if they cannot exercise self-control they should marry because it is better to marry than to remain on fire. (1 Cor 7:1-2, 7-10)
1 Timothy 4:3, far from impugning the Catholic discipline of priestly celibacy, condemns those heresies (like the Manichaeans and Albigensians) which said marriage is evil because the body is evil. Paul wasn't warning Timothy about the Cathohlic discipline--after all, Paul himself followed it!