my_list = [(11, 26), (21, 33), (90, 11), (26, 21), (32, 18), (25, 37)]

print("The list is :")
print(my_list)

my_diff_list = [abs(x - y) for x, y in my_list]

my_result = sorted(my_list, key = lambda sub: my_diff_list.count(abs(sub[0] - sub[1])))

print("The resultant list is :")
print(my_result)

The list is :
[(11, 26), (21, 33), (90, 11), (26, 21), (32, 18), (25, 37)]
The resultant list is :
[(11, 26), (90, 11), (26, 21), (32, 18), (21, 33), (25, 37)]