Living in the DC area, I feel like we have several different tourist seasons. Spring is school groups and summer is families. There are conventions year-round (pro-tip take off your badge when walking around the city)
IMHO the school groups are the worst because they travel in packs that block the sidewalk and subway doors.
I have respect for the souvenir shop on my walk to the subway because every day I see a tour bus parked out front and the store is packed with kids. My supposition is that he has cut a deal and they use his place to load the bus