Patri displicet quod frater amicis suis non parcit verbis iratis.

Because displicere works like to be displeasing to someone, not like English to dislike. In Latin, the person who experiences the feeling is often put in the dative with verbs like placet and displicet.

So:

• patri displicet = it is displeasing to the father
• more natural English: the father is displeased

The subject is the whole quod clause:

quod frater amicis suis non parcit verbis iratis

In other words, the fact that the brother does not spare his friends angry words is what displeases the father.

This is why displicet is singular: a whole clause can act as a single idea or fact.

Here quod introduces a clause meaning that or the fact that.

So it does not mean which here. It is not a relative pronoun in this sentence. Instead, it introduces the content of what displeases the father.

A good way to understand it is:

• Patri displicet quod... = The father is displeased that... / It displeases the father that...

Because frater is the subject of parcit inside the quod clause.

So the structure is:

• main clause: Patri displicet
• subordinate clause: quod frater amicis suis non parcit verbis iratis

Within that subordinate clause, frater is the one doing the action of not sparing.

Because parcere takes the dative, not a direct object in the accusative.

This is a very common thing for English speakers to ask, because English says spare his friends, where his friends looks like a direct object. Latin instead says:

• alicui parcere = to spare someone

So:

• amicis suis parcit = he spares his friends
• amicis suis non parcit = he does not spare his friends

Because suus, sua, suum is the reflexive possessive adjective. It refers back to the subject of its own clause.

In the clause frater amicis suis non parcit, the subject is frater, so suis means his own:

• amicis suis = to his own friends

If Latin used eius, that would normally mean his in a non-reflexive sense, referring to some other male person, not to frater as the subject of that clause.

Verbis iratis is ablative plural.

• verbis = ablative plural of verbum
• iratis = ablative plural agreeing with verbis

With parcere, Latin can use the dative for the person spared and an ablative for the thing in which one is sparing or not sparing. So non parcit verbis iratis means he is not sparing with angry words.

A natural English sense is something like:

• he does not hold back his angry words
• he speaks angrily without restraint
• he does not spare his friends from angry words

Yes. Non directly negates the verb parcit.

So the idea is:

• parcit = he spares
• non parcit = he does not spare

Latin often places non right before the word it most directly negates, though word order is flexible.

It is normal Latin word order, even if it feels less natural to an English speaker.

Latin often arranges words for emphasis rather than following a fixed English-style order. Here:

• Patri comes first to highlight the person affected
• displicet follows as the main verb
• the quod clause comes afterward to explain what is displeasing

So the sentence is not strange; it is just using Latin’s freer word order.

Sometimes quod can mean because, but here the most helpful understanding is that or the fact that.

The sentence is not mainly explaining a reason in the same way English because often does. Instead, it states the content of the father's displeasure:

• It displeases the father that the brother...

So for a learner, it is best to treat this quod as introducing a fact clause.