Can a Chihuahua eat tea?
NO. It contains caffeine too.
Why
Same principle as coffee, at a lower concentration. Used tea bags are also dangerous if he chews them.
What to give him instead of tea
An adult Chihuahua weighs about 3 to 6 pounds, so an amount that wouldn't bother a big dog can be serious for him. That's why there's no margin with dangerous foods: the best plan is to keep them out of his reach entirely. His diet should be built on a good-quality dry food made for toy breeds, and treats shouldn't go over 10% of his daily calories.
This information is for general guidance and is not a substitute for advice from a licensed veterinarian. Every Chihuahua can react differently; if in doubt, always check with a professional.