Heard the one about the billionaire who walks into City Hall and leaves his audience laughing?

That would be Robert L. Johnson. Everyone knows he's a cable television pioneer, aspiring major league baseball owner in Washington and, as of yesterday, would-be co-developer of a convention hotel in downtown Baltimore.

He's also a comedian.

Johnson, 56, got off a string of one-liners at yesterday's hotel announcement. For once, the often playful Mayor Martin O'Malley was not the biggest showman at the podium.

Johnson got started early with a warm-up line for all the suits and media types in the crowd. After O'Malley marveled at the coincidence that a top Johnson executive is named Tom Baltimore, Johnson jokingly pricked the mayor's bubble.

"When he goes to Denver," he said, "he's Tom Denver."

Ba-dum.

Then Johnson, who is pushing to bring major league baseball back to the nation's capital, said, "Baltimore should have everything Washington has. Washington is building a new convention hotel, Baltimore is going to build a new convention hotel."

So far, so good. Then came the zinger.

"Baltimore has a baseball team," he went on, "and Washington should have a baseball team."

Boos mixed in with the guffaws. Johnson was undeterred. "Anything you can do along that line would be helpful," he added.

So not only does Johnson want to build a hotel that Orioles owner Peter G. Angelos passed on developing himself, but there he was at City Hall talking up a baseball plan that Angelos strenuously opposes.

But Johnson wasn't done. When a reporter asked about the germ of the hotel deal, he stepped to the microphone and said, "I'll be the germ."

He proceeded to give credit to various individuals but did not want to leave out Catholic Relief Services. The nonprofit group plans to put a new headquarters adjacent to the hotel.

Or as Johnson put it, "And then you got God over here" wanting to build new offices. With a combination like that, he said, "You can't fail."