who let themselves be f***ed in the ass by saintly motorcyclists, and screamed with joy,
They had sex with bikers and loved it.
We've already seen how several unusual types of people have been compared to saints, angels, and other holy figures, and here the motorcyclists are called "saintly." Ginsberg used religious language in new and unexpected contexts, which he hoped would make people reconsider traditional ideas.
By the way, this is one of the lines that caught the attention of government censors and led to the famous trial involving Howl.
who blew and were blown by those human seraphim, the sailors, caresses of Atlantic and Caribbean love,
In addition to sex with motorcyclists, they also exchanged oral sex with sailors on leave.
As in line 35, this line combines religious language ("seraphim" are an order of angels) with blunt descriptions of sexuality. This line was also cited in the censorship trial.
who balled in the morning in the evenings in rose gardens and the grass of public parks and cemeteries scattering their semen freely to whomever come who may,
They had anonymous sex with strangers in public gardens and parks.
Before homosexuality acquired wider acceptance in society, gay men sometimes found partners in certain remote public areas within places such as parks.
who hiccuped endlessly trying to giggle but wound up with a sob behind a partition in a Turkish Bath when the blond & naked angel came to pierce them with a sword,
A "Turkish Bath" is another place where men sometimes had anonymous sexual encounters with one another.
The "best minds" were trying to laugh but ended up with a sob instead.
And "sword" is a phallic reference.
who lost their loveboys to the three old shrews of fate the one eyed shrew of the heterosexual dollar the one eyed shrew that winks out of the womb and the one eyed shrew that does nothing but sit on her ass and snip the intellectual golden threads of the craftsman's loom,
The speaker is talking about how the three ways in which they lost their gay lovers. The "three old shrews of fate" is an allusion to the Three Fates, mythological goddesses who decided when a person's life would end by cutting a thread.
The speaker is suggesting that the men lost their "loveboys" to metaphorical women. Strangely, these women have "one eye," which suggests phallic imagery.
The first such shrew is the "heterosexual dollar," which probably means that the boys gave up being gay for the sake of their careers.
The second "winks of out of the womb," which probably means that the men got their girlfriends pregnant.
The third sounds like a parody of a wife who "does nothing but sit on her ass." As in, the boys got married and had to give up their male lovers. She may be an allusion to Penelope, the wife of Odysseus in the The Odyssey, who spent a lot of time sewing at her loom. But, of course, the "threads" also refer back to the idea of death and the Fates.