"Today, fans can range from fair-weather to those that 'bleed' their team colors," Bissot says. "Just like the involvement in certain associations and groups can help build immediate trust and rapport with a client, picking the wrong team can lead to distrust, aversion and lost business."

In today's workplace, Bissot says it is a dangerous game to try to determine the level of passion and commitment of a fan.

"Ultimately, it is simply not worth the risk. Employees should look for clues like any logos in a client's office or use general conversation about sports to find out more before ever bringing their team, or sports in general, into the picture."

On the flip side, John Greene, president of CSB Training and chief operating officer of Collaborative Consulting, says that once you know your clients well, supporting the right team -- or having a friendly rivalry -- could earn you a few football season brownie points.

"I would never worry about offending a client by rooting for your own team," Greene says. "If the client is sports-oriented they will understand. In fact, I have seen it work in our favor by creating a fun and healthy rivalry when you're playing the client's team in a big game. It helps build relationships."

Unfortunately, most team apparel isn't exactly professional. While it's possible to find items such as logo ties for men or jewelry and purses for women, largely fans gravitate to T-shirts, tank tops, flip-flops and other items that are a no-go for many workplaces no matter the occasion.

"I would never recommend wearing anything more casual than the dress code, that's where you can definitely send a negative message," Greene says. "On this one, following the rules makes sense. While an occasional slip-up won't seriously hurt you, constantly ignoring the dress code will."

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