Harbaugh himself was accused by Sherman and Seattle safety Earl Thomas of honking and mockingly saluting at Seattle's team bus on its way out of San Francisco in 2012, though Harbaugh has denied it. And San Francisco assistant coach Greg Roman was once heard shouting, "Merry Christmas!" inside the Seattle press box after a 49ers victory there in 2011. Even Harbaugh's wife, Sarah, once admitted on a television interview that, "I really don't like Seattle at all."
But underneath all the silly exploits and the trash-talking that capture headlines from time to time, there is also -- believe it or not -- a respect level that has grown between these two teams over the past three years since Harbaugh took over as San Francisco's coach.
Each recognizes that the other is its stiffest competitor.
San Francisco linebacker Patrick Willis compared the rivalry to a "heavyweight fight" this past summer, saying, "We're not throwing little jabs that barely hurt. We're trying to knock each other out."
And Willis reiterated this week that "there's no question there's a lot of hostility between us."
Willis did add, however, "If we weren't in this race right now, there'd be no doubt that if they were playing against someone else, I would wish them well, because it's in our division. But it's us playing, so there's not going to be any like at all there."
Adding to the unique nature of the rivalry is the striking similarities between the two teams, which value hard-nosed, physical defense and a power run game above all else -- and which both reshaped their identities by adding electrifying young quarterbacks, Russell Wilson in Seattle and Colin Kaepernick in San Francisco, to the mix last year.
And more than ever this year, the front offices keep poaching players from the back end of the other team's rosters -- which is probably an indication of the bad blood between the franchises, but also an indication that they simply have the same taste in players. After all, former 49ers general manager Scot McCloughan, who helped build a good chunk of San Francisco's roster, is now an assistant in Seattle's personnel department.
The teams' personalities are a little different -- they tend to mirror the personalities of their head coaches. Harbaugh is as intense as it gets, while Carroll keeps it loose. San Francisco is more buttoned up, while Seattle's players are by far the more outspoken and vocal ones. They're more of a "chip on our shoulder" team that many observers believe is still clamoring for some level of national respect.
Over the past two years, the home team has won each game in the series. Seattle has some bragging rights because both of its wins have been blowouts. But the 49ers hold the ultimate bragging rights since they reached the Super Bowl last year.
There aren't too many examples of the bad blood spilling over into on-field fisticuffs or cheap shots. They have, however, managed to rack up a combined 19 flags for unnecessary roughness, unsportsmanlike conduct or taunting during their past six meetings, as their physical styles and intensity are constantly on display.