"Behold what manner of love the Father hath bestowed upon us, that we should be called children of God; and such we are. For this cause the world knoweth us not, because it knew him not." (ASV)
Many Christians are timid about sharing their faith, or even letting the world know that they are Christians. They afraid of what a secular world will think, say or do. They don't want to offend non-believers by proclaiming that God exists and He loves them. While it is true that many people may make fun of us, or even get angry with us because of our faith, that is no excuse for becoming a closet Christian.
The world does not understand Christianity. They won't until the day of Christ's return when "every knee shall bow, every tongue shall swear." (Isaiah 45:23) They can't understand Christians until they begin to understand Christ. So yes, if you tell your coworkers about God, you may hear giggles in the lunch room or be stared at by some of them, but is that so high a price to pay?
Christ made it very clear that He wants us to talk about Him and about our faith. "Every one therefore who shall confess me before men, him will I also confess before my Father who is in heaven." (Matthew 10:32) He wants us to let the world know that we belong to Him, and this is not because He was not able to foresee the reactions we might get. Rather, He had this advice for those who face persecution in His name: "Rejoice, and be exceeding glad: for great is your reward in heaven: for so persecuted they the prophets that were before you." (Matthew 5:12) And the ridicule or judgement of our peers is a far lighter sentence than the persecution He spoke of.
In the end, when we choose to hide our faith, we are telling God we are ashamed of Him. We are not willing to be associated with Christ, who bled and died and defeated even death for our sake. Instead, we should be shouting from the rooftops that Christ is Lord and we are His!