is giving my dog my leftover tea(drink) bad for him?

I wouldn't worry too much.

Mine have been getting the last few licks of my coffee and tea for years and they are perfectly healthy.

Coffee, sugar and tea aren't good for a dog but in that small of an amount it's not going to hurt. It's only dangerous if you let them drink a whole cup of it or give them a bag of coffee grinds to chew on.

If it's caffeine-free and isn't loaded with things like sugar, cream or artificial sweeteners, it's fine, so don't worry. If it contains caffeine, avoid giving it to him because caffeine and dogs don't mix well. Caffeine is a stimulant that raises their already quick heartbeats and affects their nervous system, and due to your dog's relatively small size, it doesn't take much caffeine at all to pose as a threat. Additives like sugar and cream aren't as dangerous, but they're definitely unnecessary in your dog's diet, and too much can easily lead to such things as tooth decay and weight gain. Artificial sweeteners can be dangerous for dogs; some, like xylitol, for example, can fatally poison your dog.

YES. Tea contains Caffeine naturally. Which can be very bad for your dog. He only needs water, nothing else.

You shouldn't let your dog drink it if it has sugar, artificial flavors and sweeteners, and caff in it. White tea has no caffeine as well as peach tea, orange tea, cranberry tea.

Yes, the caffeine is very dangerous to your dog. It can cause serious problems with the cardiovascular system.