According to a Catholic interpretation of the Bible, was Jesus being glib in Matthew 6:34? When Jesus says "Sufficient for a day is its own evil," was Our Lord making light of the fact that a lot of bad stuff happens every day?   

I'm reading this as part of a scripture study with some scouts tomorrow and I'd like to know what Catholic commentators and saints have to say about this, and the particular attitude that a line like this would be stated with.
You might look at the commentary of St. John Chrysostom, who is a 4th century Saint and Doctor of the Roman Catholic Church.  He explains in his 22nd Homily on the the Gospel according to Matthew:


  By evil here He means, not wickedness, far from it, but affliction,
  and trouble, and calamities; much as in another place also He says, Is
  there evil in a city, which the Lord has not done? nor any thing like
  these, but the scourges which are borne from above. And again, I, says
  He, make peace, and create evils: [Isaiah 45:7] For neither in this
  place does He speak of wickedness, but of famines, and pestilences,
  things accounted evil by most men: the generality being wont to call
  these things evil. Thus, for example, the priests and prophets of
  those five lordships, when having yoked the cattle to the ark, they
  let them go without their calves, [1 Samuel 6:9] gave the name of evil
  to those heaven-sent plagues, and the dismay and anguish which thereby
  sprang up within them.
  
  This then is His meaning here also, when He says, sufficient unto the
  day is the evil thereof. For nothing so pains the soul, as carefulness
  and anxiety. Thus did Paul also, when urging to celibacy, give
  counsel, saying, I would have you without carefulness.
  
  But when He says, the morrow shall take thought for itself, He says it
  not, as though the day took thought for these things, but forasmuch as
  He had to speak to a people somewhat imperfect, willing to make what
  He says more expressive, He personifies the time, speaking unto them
  according to the custom of the generality.