I'm afraid I don't agree with Dot on this one.
Warnings are invariably given for either Conduct or Capability. The former is 'your behaviour is not good enough' and the latter is 'your performance ain't up to the mark (including 'you keep being off sick')
If someone was given a warning for, saying, fighting, that's Misconduct. That person gets a written warning for misconduct and the letter will say something like in the event of your misconduct in the next 12 months, further disciplinary action may be taken that may lead to your dismissal.
So if 6 months later they get up to some silly or dangerous prank, that's also misconduct. Two events, and the potential for dismissal, but very dependent on the circumstances.