"Down to Ride"
If someone is DTR, it means that they are excited to do basically anything. This is especially true of situations of craziness, ridiculousness, randomness, and spontaneity.
DTR can be a lifestyle. It can also be a mood.
me - "Hey, we're not doing anything... Wanna go light some stuff on fire?"
friend - "Sure, man! I'm DTR!"
me - "Later we can go climb some buildings and point laser pointers at drunk people!"