You could try taking something IBS safe to share with your co-workers. Maybe muffins or a quick bread that you can slice & share with them. There are a lot of recipes on this website. And if you don't like to cook, sometimes you can find IBS safe stuff at the HFS or grocery store. That way they'll see that you do want to participate, you just can't have certain foods.
-------------------- IBS-A...I can never make up my mind