Stanza 1 Summary

Get out the microscope, because we’re going through this poem line-by-line.

'TERENCE, this is stupid stuff:

The first voice we hear in this poem might surprise you a little. He's bold, to the point, and a little crass. He (and we're just assuming it's a he here, since Houseman was a he and we don't have anything else to go on) doesn't refer to "unpleasant objects" or "disagreeable discourse" like a fancy poet might. He comes right out and calls it "stupid stuff." (At the same time that little bit of alliteration in "stupid stuff" is a reminder that this is still very much a poem).
So who is this guy? Well, be sure to notice that little mark at the beginning, before "Terence," which means the start of a quotation. The whole first stanza of this poem turns out to be a quote from a guy who's talking to the poet, whose name is…(three guesses) Terence.

You eat your victuals fast enough;

Here the guy we met in the first line keeps talking, and keeps us focused on simple things. He points out that Terence is doing just fine wolfing down his "victuals" (that's an old-fashioned word for food).
Be sure to notice that, even though the character who's speaking now is pretty plainspoken, his lines are still written in even, regular poetic meter. This line is a great example of iambic tetrameter, which is the basic meter for this entire poem. That just means that the line has four pairs of syllables, with the stress falling on the second syllable of each pair. Come again? Check out "Form and Meter" for all the skinny on this sort of stuff.

There can't be much amiss, 'tis clear,
To see the rate you drink your beer.

Here the fellow talking to Terence keeps up the comments. He's teasing Terence, pointing out that the poet can't be feeling all that bad if he's knocking back the beers as fast as he is. This is a friendly, barroom chat, one guy needling the other, just like folks do in a bar today.
Housman does a good job of making us hear the voice of the speaker in these lines. For example, this guy definitely steers away from big words. Every single word in these two lines is one syllable long—no fancified phrases for him.

But oh, good Lord, the verse you make,
It gives a chap the belly-ache.

Now the speaker gets to the point, and tells us what his gripe really is. The food and beer might be going down fine, but Terence's "verse" (his poetry) gives the speaker a "belly-ache." It's the poetry that he thinks is "stupid stuff" (1). He doesn't tell us why yet, but trust us, he's about to. This dude doesn't mind giving us a piece of his mind.
The speaker is still sticking to rough, plain language, with expressions like "good Lord" and "chap" thrown in. At the same time, we feel like it's only fair to point out that, even if this guy doesn't like poetry much, he's definitely speaking in a poetic style. By now you've probably noticed that the lines of this poem make perfect rhyming pairs: "clear" rhymes with "beer," "make" with "ache" and so on. We call that pattern rhyming couplets.

The cow, the old cow, she is dead;
It sleeps well, the horned head:

Our poetry-hating friend is really getting going now. He starts to make fun of poetic style, and in these lines he does a pretty funny parody of a sad poem about a cow. He's teasing Terence about the pointlessness of his subjects (who wants to read a poem about a dead cow?). At the same time, he's also mocking the repetition ("The cow, the old cow") that's so common in poems and the fancy words like "horned" which you have to pronounce as two syllables (horn-ed) to fit the meter of this poem.
For this guy, a dead cow is a dead cow. Why would you discuss it, much less dress it up in fancy terminology?

We poor lads, 'tis our turn now
To hear such tunes as killed the cow.

Another little joke from the speaker, who says it's "tunes" (verse) like Terence's that killed the cow. Now the "poor lads" at the bar have to be subjected to the same sad, mopey poems.
Pairs of lines like this are held together in this poem by the fact that they rhyme ("now" and "cow"). On top of that, they tend to hold together as single ideas and complete sentences. So, in the first half of this rhyming pair (line 9), the sentence continues past the end of the line (that's called enjambment). But then, when the couplet ends in line 10, the sentence ends, too. You'll see this pattern repeating all through the poem—it's one of the things that anchors the poem and gives it its structure.

Pretty friendship 'tis to rhyme
Your friends to death before their time

The teasing continues, as the speaker protests that Terence is going to kill them with his sad poems, just like he killed the cow.
"Pretty friendship 'tis" just means something like "some friend you are!"
These lines keep up the theme of jokey poetry-hating. At the same time, they reinforce the feeling that this is all just in good fun, since the speaker acknowledges that he and Terence are friends.

Moping melancholy mad:
Come, pipe a tune to dance to, lad.'

Line 13 is another dig at poetic style. Here the speaker is making fun of that favorite poetic trick, alliteration. By referring to Terence's poems as "Moping, melancholy, mad," he can tease him for both the depressing content and the funny form of his verse.
The speaker finishes the stanza (and his speech) by telling Terence he wants to hear something entertaining. He wants him to pipe (that means to play on a musical instrument) something he can "dance to." He'd take a happy song over a "melancholy" poem any day.