Yes, sometimes people do take a verse or so out of the Bible and twist it to mean something totally different from what God intended. But does that make the Bible useless or undependable? No, of course not. Sometimes people try to twist the meaning of a particular law–but that doesn't invalidate our legal system.
If your friend is sincerely open to what the Bible teaches, you can help him understand why he can trust the Bible–through the discoveries of archaeology, for example. Jesus said in one of His prayers to His Father, "Your word is truth" (John 17:17).
Frankly, however, most people who laugh at the Bible aren't really interested in finding out why they can trust it. Their real problem is that they don't want to turn to God–and down inside they are afraid that if they begin to take the Bible seriously, God may confront them with their sin and their need of Christ.
What can you do? First, pray for your friend, for only God can open his heart. Then ask God to help you demonstrate by the way you live that Christ is real, and He offers us a new life. Do others (including your friend) see Christ's love and joy in you? Finally, as God gives you opportunity, share with your friend what Christ has done for you–and can do for him.