How we cite our quotes: (Chapter.Paragraph)
Quote #1
Still the bouncing had some physiological effect. Ignatius touched the small erection that was pointing downward into the sheet, held it, and lay still trying to decide what to do…. he thought somewhat sadly that after eighteen years with his hobby it had become merely a mechanical physical act stripped of the flights of fancy and invention that he had once been able to bring to it. (2.14)
Again, unsexy sex is funnier than sexy sex. In this case, the sex is doubly unsexy, in that it's masturbation rather than sex, and in that it's sad or diminished. Ignatius is nostalgic for the unsexy sex he once had.
Quote #2
"You two might of settled down and had a nice baby or something."
"Do I believe that such obscenity and filth is coming from the lips of my own mother?" Ignatius bellowed. (2.245-246)
Usually you don't think of settling down to have a baby as obscene, but Ignatius is very sensitive. It's also worth pointing out that he is very much his mother's son. Mrs. Reilly remembers Ignatius's conception as something shocking, if not as actually obscene, so Ignatius may well have picked up his Puritanism from her.
Quote #3
Suddenly Mrs. Reilly remembered the horrible night that she and Mr. Reilly had goen to the Prytania to see Clark Gable and Jean Harlow in Red Dust. In the heat and confusion that had followed their return home, nice Mr. Reilly had tried one of his indirect approaches, and Ignatius was conceived. Poor Mr. Reilly. He had never gone to another movie as long as he lived. (4.94)
This is the closest we get to a description of sex in the novel, and it's precipitated by a film (Red Dust, from 1932). Ignatius was conceived following a movie—and so his love/hate relationship with film perhaps mirrors his father's love/hate relationship with film, in a kind of Oedipal reflection. Ignatius hates the movies and loves their decadent, sensual appeal, just as his father responded to the decadent, sensual appeal and then hated himself in the morning. There's more on this over in the "Symbols" section.