In this film clip one of the characters says "I'm jacked... I'm jacked to the tits!!!" - what does this mean in this context and other contexts?
In this context "jacked" is a slang term similar to "high", meaning "under the influence of a powerful (usually illegal) drug. If I had to guess at its origin, I imagine it's a picturesque metaphor of your body plugged into an electrical socket, and therefore "full of energy" or "lit up". So it's most often used to refer to the use of drugs that make you feel especially powerful or energetic (like cocaine or perhaps steroids).
"Jacked to the tits," is a colorful metaphor that simply means "very high". In this film clip I don't know if the character is actually under the influence of a drug, but he feels as if he is high -- he's almost uncontrollably excited.
You should be careful not to confuse this with other slang terms that use "jacked". In some dialects, "jacked" or "jacked up" means "to have some injury or incapacity". For example, I could say something like:
I woke up this morning and my neck was jacked up (my neck hurts). I must have slept weird.
She ran her car off of the road and her body was jacked for months after.
Of course, you can use both, for fun:
He was totally jacked last night but after he came down he was jacked up all the next day.
There are other slang uses of "jacked". In some contexts it can mean "stolen" (as an abbreviation of "hijacked"):
Dude! My car got jacked last night!
Or as previously mentioned, as the verb meaning "to plug into an electrical outlet" (based on the noun "jack: a female fitting in an electric circuit used with a plug to make a connection with another circuit"):
Hey could you jack my guitar into the amp?
It's a fun word. Remember, though -- slang isn't universal. I don't know if these meanings will translate anywhere English is spoken. Also it's constantly evolving, so terms can take on a different nuance over time.
Here is a list of various other definitions for "jack", although even this is not complete