In an office or a home, if your host asks, “Would you like tea or coffee?” the person is actually asking you “which” you want, not “if” you want it. So do not say just “Yes.” It is proper to reply with your choice: “Tea would be nice, thank you. or “I would enjoy a cup of coffee.” or “No, thank you.” If you do ask for coffee, you may also be asked, “Regular or decaffinated (decaf)?” Reply with your choice.
The Japanese custom of offering something three times and refusing it three times does not hold true abroad, so if you are counting on the person repeating the invitation three times, you will end up without a drink.
The Japanese custom of enryo is very nice in Japan, but it seems unnecessarily tedious in the United States. If you are offered tea or coffee and reply, “Whichever you are having,” you are not helping the other person. He or she has offered the possible choices and all you have to do is tell which one you would prefer, or simply decline with “No, thank you.”