the fear or reluctance of dialing the last digit of a phone number; seen most commonly among guys who get the number of a girl they like and want to ask out, but then fail to muster up enough courage to complete the call, usually stopping before punching in the very last key of the number.
Dude #1: "Denise gave Adam her home phone number, and he was so stoked about it he said he would give her a call last night. But I guess he must be suffering from last digit syndrome, since all he kept dialing was "555-236...and it stopped there every time!"
Dude #2: "Ha! well hopefully he'll grow a set by tonight and try again....hotties like Denise don't stay single for very long, ya know!"