This play begins in the middle of a war and (spoiler alert) ends in the middle of a war. Pretty depressing, really. When Hector is slaughtered by Achilles and his Myrmidons (and then dragged through the fields by a horse), Troilus predicts that Troy will soon fall to the Greeks.
So, Hector's death should be where the play ends. But Shakespeare doesn't end on this tragic note. He wants us to feel even worse, so he sends Pandarus on stage to deliver a nasty speech that's as bitter as the rest of this play. Basically, Pandarus tells us that he's dying from a sexually transmitted disease as he gives a weird shout-out to all his fellow "traders in the flesh" (a.k.a. pimps). This seems kind of odd until we remember that Elizabethan theaters were in the same neighborhoods as brothels, so there probably were a few "bawds" in the audience.
And then it gets even weirder. At one point in the speech, Pandarus starts talking to us like we (the general audience) are all his "brethren and sisters" in the sex trade industry. Huh? Finally, he tells us that when he writes his will, he's going to "bequeath" us all his "diseases." Yep. Pandarus says he hopes we all get an STD and die, even though he thinks we probably already have syphilis.
What's going on? Well, it seems to us that Shakespeare's play is telling us that humanity in general is nothing more than a big lump of "disease[d]" flesh. Thanks, Shakespeare. We love it when you tell us mankind's future is totally bleak.