Is Ruby able to understand in-line comments like:
my_array = ['first', /* 'second', */ 'third', 'fourth']
No, Ruby does not have inline comments.
Comments of this style have a tendency to reduce readability, since they makes the code harder to follow.
In your case it would be best to split your array items into separate rows and comment out the one row.
my_array = ['first', # 'second', 'third', 'fourth']