You were using a terminal off the payphone, or are you just trying to be humorous?
Though a deaf relay op is obligated to not interfere with a call, I'm pretty sure they COULD report harassment on a terminal. You should be fine as long as you don't go back there and as long as you didn't give out any private info on the call, though I'm not sure if they could give that out anyway.
If you were to get busted, you could be charged with harassment (maybe), and the relay company may be able to press a civil charge for abuse of services, but I don't know if either would stick. The only person I know who got hit with something like that sent a bomb threat via IP-tty from a school computer lab to the school.