You should use { }.
Code:
on me:*:JOIN:#:{ msg $chan Hyper is Back }
on !*:JOIN:#Crazy:{ msg $chan Welcome $nick to Crazy Channel. }

on *:JOIN:#:{
  if ($nick == $me) { msg $chan Hyper is Back }
  elseif ($chan == #Crazy) { msg $chan Welcome $nick to Crazy Channel. }
}