Try using double speech marks around your text, and a space between your end and if on your last line, also the last else if only needs to be an else statement, plus the objectid field is numeric so you don't need the values in speech marks.
DIM temp as String
IF [OBJECTID] = 1 THEN temp = "Very Destructive"
ELSEIF [OBJECTID] = 2 THEN temp = "Destructive"
ELSE [OBJECTID] = 3 THEN temp = "Damaging"
END IF