So, Jerk Ford. What would happen if he was given truth serum and pressed for his real thoughts? I'm guessing there would be exactly zero change except maybe with Stanley
Also, does the existence of Jerk Ford imply that there's a Jerk version of everyone else?
Jerk Ford is not necessarily a liar, that's his brother Stan.
He will re-word or re-frame things to make a different point, he will ommit information, but he will not straight up lie. Lies by ommission? Plenty.
Lying to himself? Even worse. His genius brains ability to gaslight itself is so strong that he has an insane pain tolerance despite his nervous system being completely intact.
Chronic pain causes brain shrinkage, and to avoid that his unconscious mind convinced his conscious mind that there is no pain. Because of his constant, terrible pain he was in while in the multiverse, especially before he perfected his Regenerative Serum. He does not literally lack the ability to feel pain; his brain just refuses to acknowledge / process pain signals from his nerves.
But yeah he'll tactically avoid confessions under a truth serum by using non-lies and flowery, deceptive language. He is known for his wit after all (among other things).
As for the existence of a 'Jerk Version' of everyone else-
Any given trait across the multiverse is on a scale. Even if most Stanford Pines variants are geniuses, you get versions who aren't as smart, who are even more smart, or their intelligence is in fields other than science.
And its the same for any other trait - a scale where there's always one at both extremes.
The kindest, the least kind. The most Filbrick-like, the most removed from Filbrick as possible, the tallest vs the shortest, ect. The frame of reference is Canon Ford, who is at the epicenter of all of these scales and ranges.
Jerk Ford is not different from Canon Ford because his dimension is at the extreme jerk end of the jerkiness scale - his Dimension is different from canon because he is at the extreme jerk end of jerkiness for Stanford Pines variants.
There is a Jerk Dimension with it's own version of Stanford Pines - but it's not a dimension full of jerks, it's just the only dimension where beef jerky isn't expensive.
(That Ford does get mixed up with his more infamous counterpart, however).