It's common in improv workshops to warn the actors not to "think too much." This is because it's generally believed that the rational, language-oriented left half of the brain inhibits spontaneity, and that the best improv rises from the intuitive depths of the brain's right half. Leave it to the ever-rebellious Annoyance Theatre to create a fully improvised show in which being too rational is the point: Modem Problems in Science. Every Tuesday evening Dick Costolo, Rich Fulcher, and Phil Granchi conduct a completely bogus science demonstration to "prove" whatever oddball thesis the audience tosses out: that "ugly things fall faster than pretty things," that the "Apollo 11 was powered by Cap'n Crunch," or (the night I saw the show) that "the earth is shaped like a giant burrito." Not since Severn Darden delivered his ponderous, droll lectures at the Second City in the early 60s have improvisors waded so deeply (or so successfully) into these murky intellectual waters. Using every intellectual weapon at their disposal--sarcasm, outrageous puns, digressive story telling, exceptionally complicated diagrams on the blackboard--these funny, verbally facile performers spoof sloppy thinking, popular culture, and the foibles of academics--and draw sellout crowds on a Tuesday night. Their secret? They think too much, therefore they are too much. Annoyance Theatre, 3153 N. Broadway, 929-6200. Open run: Tuesdays, 8 PM. $5; $7, or $5 with a can of food for donation, for both Modern Problems in Science and Spankin' Time (see listing) later the same evening.