Hey, baby, wanna do some tea?

However, it is good for a joke, especially if you're a foreigner; nobody will expect you to know this lovely phrase. It'll get a laugh every time. Well, no, I take that back. It'll get a laugh the first time. Then don't ever use it again.

If you would actually like to drink some tea together, try this phrase:

Ocha demo nomi ni ikimasen ka?
Would you like to go get some tea or something?

Another good, honest line you could use after the aforementioned tea, or perhaps after a party where you just met.

Sukoshi arukimasen ka?
Would you like to walk for a bit?