An if statement should get the flood to work. Try:

Code:
 
if ((%floodscarywave2) || ($($+(%,floodscarywave2.,$nick),2))) { return }
  set -u300 %floodscarywave2 On
  set -u300 %floodscarywave2. $+ $nick On


This code makes it so that there has to be a 5 minute gap between any new person using the command, and also a 5 minute gap from anyone one person using it. I'm not sure that's what you intended, but I kept your same flood time.