NEW YORK, Jan. 29 - One of our nighttime disc-jockies, Jean Shepherd, hovers between whimsy-and-profundity. Over the Mutual Network he insists folks do their best thinking at night, because we're too rushed for time during the day. The drive to "make it yourself" has got us all doing rather than thinking. From 15:30 a.m. to 5:30 a.m., seven nights a week, Jean Shepherd delivers a volley of words that furrow the forehead and convolute the brain. For instance, "If you were getting yourself tattooed, what tattoo would you choose? Clasped hands? A pair of joined hearts? A rose? A snake? Your sweetheart's initials? Your fraternity letters? . . . We know what's a highbrow and what's a lowbrow, but what's a middle-brow? . . . A beautician has suggested that women take wine baths. Whether they bathe in port, Rhine wine or purple grape, can you imagine how awful they would smell? Despite ambitious merchants, these winey ablutions could not fail but to revolt. "THE TWO most recognized 20th century sounds in the United States are," according to Shepherd, "the sound of a spoon stirring coffee in a cup and ice cubes clinking in a drinking glass. The third sound would have been taxi horns had not many cities declared horn-honking a violation . . . The phrase 'sipping Wine out of her slipper' is often used but has anyone actually ever been seen drinking out of a supper? "The State of Vermont is pouting at the State of New York, because Gov. Harriman has declared the sugar maple the official tree of the State of New York. Everyone knows that Vermont and maple sugar go together like love-and-marriage. We have so many magnificent kinds of trees in New York State, why can't New York generously allow Vermont exclusive rights to being 'Miss Maple Sugar*? The New York State tree should really be that tree which grows in Brooklyn, the ailanthus. "BESIDES ENCOURAGING youngsters to love guns and imitate bad men, TV is accused by school teachers of having a bad influence on children's language. Many adults on television talk down to children. They drop "h's," use poor grammar like, 'It's got all them vitamins.' "Also they mispronounce words like 'Send 25c for an autographed pitcher.' Such small fry talk is not to the taste of today's educators.