Each clue is a Latin phrase as it might be interpreted by someone who doesn't really know any Latin.
| One who doesn't say "thank you" | PERSONANONGRATA |
| Rental company that's hard to find | RARAAVIS |
| Wagon that attracts things | MAGNACARTA |
| Lament from "On the Waterfront" | NOLOCONTENDERE |
| Fishing holiday | CARPEDIEM |
| Poem about one's foibles | VICEVERSA |
| Warning when you're almost out of gas | CAVEATEMPTOR |
| Why everyone hears when spring ends | SUMMACUMLAUDE |
| Between SDTV and HDTV | INMEDIASRES |
| Why thinkers become accountants | COGITOERGOSUM |
| Italian gaming convention | PAXROMANA |
| Druopta Efekta, e.g. | CAMERAOBSCURA |
| Where the cause of some teenage grief lies | INLOCOPARENTIS |
| Former place of worship | EXCATHEDRA |
| Crucial course material | CURRICULUMVITAE |
| Like fans of U2 concerts | PROBONOPUBLICO |
| A really, really long commercial break | ADINFINITUM |
| Two, three, or five on a die | PRIMAFACIE |
| Opposite of a lax tenon | RIGORMORTIS |
| How one sits | APOSTERIORI |
| Like an unfinished clock tower | ANTEBELLUM |
| Al Qaeda's legal team, e.g. | TERRAFIRMA |
| Result of starting a sit-up regimen | ABINITIO |
| What non-amateurs get paid | PRORATA |
| Solution to: x2 + cos2(0) = 1 | SINEQUANON |
| To pursue a non-specific lawsuit | SUIGENERIS |
| The result of further radiological dumping | MUTATISMUTANDIS |
| "The Pony Express began in April 1860," e.g. | EXPOSTFACTO |
The indicated blanks in order spell NICODEMUS GOSPEL ON CORE FITNESS. The Gospel of Nicodemus does not contain anything about the Pilates fitness system, but it does contain a text known as the ACTA PILATI, which is the answer.