- Booing a pitcher for trying to pick off a runner. No matter which team is pitching, this is not cool. In fact, booing in general should be reserved for only the most heinous on-field crimes, or maybe off-field events such as a player's moving to a rival team due to free agency.
- Corollary: booing any player on your own team is not ok, unless he just ate a puppy on the field or something similarly awful. A batter repeatedly chasing bad pitches or two outfielders colliding and dropping a routine fly warrants a disappointed "ohhh" or an aggrieved "come on, man," but not booing.
- The Wave. It looks stupid in a diamond-shaped ballpark. Leave it for European soccer hooligans. This counts doubly for the ancient temples of baseball such as Wrigley Field and Fenway Park, where The Wave ought to be grounds for immediate expulsion.
- The words "offense" and "defense." I believe the words you're looking for are "batting" and "fielding." "Pitching," too. Admittedly, I'm no authority in the subject, and "offense" and "defense" aren't strictly wrong, but they just seem ill-suited to baseball.
- Jumbotron messages telling the crowd to "make some noise" at critical moments. If you were paying attention to the game, you'd know when extra cheering is appropriate. If you're not paying attention to the game, why are you there?
- Leaving early if your team is losing. Maybe it's okay to leave early if your team is being crushed and it's raining really, really hard. Worse yet, some people leave early even when their team is winning - presumably to "beat the rush." Why did you bother coming to the game at all?
- Crying. There's no crying in baseball.
Lest this be solely a series of complaints, I'll conclude with my favorite baseball moments.
- Once, at the Metrodome, Lisa kicked another fan in the head while getting into her seat. The kick was an accidental tap against the noggin of a gentlemen seated in the row ahead of us, and she apologized profusely. He laughed it off and joked, "now you owe me a beer." Later, Lisa actually did buy him a beer, and the surprised gentleman tipped his cap, his faith in humanity no doubt restored.
- The Miller Park Sausage Race is the best break-in-the-action entertainment ever. Grown men wear costumes representing various meat products and run around the field.
- Any time the Cubs play a night game on the west coast while Lisa and I are driving to Minnesota. Thanks to the joy of AM radio propagation at night, we can pick up WGN all the way to the Twin Cities. Regardless of the team's performance, Cubs radio broadcasting is top-notch. Also, Lisa loves Ron Santo.