At Theatre 99 on Thursday night (the late set at 10 p.m.), Big Dicktionary’s joyful meandering started with a low mumble and rumble and gradually escalated into fully-blown psychotic break.

The improvisational comedy duo of Timmy Finch and John Brennan have been doing this unpredictable long-form ramble for a while now, so the on-stage chemistry between them is impressive, to say the least.

At the set’s opening, both walked out on stage with Finch carrying an oversized Webster’s dictionary. Brennan poked his into the pages and randomly picked the lead-off topic — the Santa Fe Trail in western Missouri. Right off the bat, the two grabbed their folding chairs and eased into “character” as two dudes on a wagon train … which detoured into a scene with a teenager on a moped with two weird cops … which detoured into a scene with Joseph and a Mary (one of the wagon train dudes in drag, actually) and a naughty re-enactment of the Nativity … which detoured into a scene with two coke-snorting Senators arguing over pop culture and classic TV shows … which detoured into a scene about Sesame Street’s Cookie Monster and Oscar the Grouch … which detoured into the moped kid’s straggle with his inner demons … etc.

It was wild, weird, and very funny. Finch, in particular, was very sharp, hyper, and animated, while Brennan (who sometimes emulated actor Patrick Swayze’s wind-blown machismo in Wednesday’s performance of The Banana Monologues) seemed more at ease … like a smirky Steve Martin doing a Robin Williams impression. —T. Ballard Lesemann