In Romans 14:14 Paul makes clear that what we eat or drink is not sinful in itself: “I know and am persuaded in the Lord Jesus that nothing is unclean in itself, but it is unclean for anyone who thinks it unclean” (ESV). Nevertheless, for a Christian to do something he believes is wrong is a grievous sin. Thus he warns, “Do not, for the sake of food, destroy the work of God. Everything is indeed clean, but it is wrong for anyone to make another stumble by what he eats.” (v. 20).
In other words, Paul is not simply admonishing Christians not to do things (specifically involving eating or drinking) which might be displeasing to fellow believers. Rather, what the strong are to avoid is encouraging the weak to do something which, though not wrong in itself, is believed by the weaker brother to be wrong, and in which the activity of the strong might encourage the weaker brother to sin against his conscience. As John Murray summarizes, “The stumbling and falling implied refer to the doing on the part of the weak of what is contrary to their conviction. The weak are induced to do what they are not yet able to do in faith and with a good conscience. Thus they wound their weak conscience and sin against Christ.” (“The Weak and the Strong”). You may not, you must not, by your words or actions encourage your brother to do something he believes to be sinful.
Although Murray argues persuasively that Paul’s point is not to avoid activities which some believers might consider offensive, he adds an apt reminder: “It goes without saying that Christian courtesy will often dictate abstinence from certain things out of deference to the wishes of others, especially of Christian brethren whom we love in the Lord. Considerateness is a virtue much to be coveted and practised.”
In short, glorify God and show love to your fellow believer!