In a medium bowl, toss together cucumber and red onions.
Mix sour cream, mayonnaise, garlic, white vinegar, dill, black pepper, and sugar in a separate bowl. Avoid mixing vigorously or beating the mixture; otherwise, it will become thin inconsistency.
Now pour the dressing over the vegetables and toss them well until vegetables are coated.
Refrigerate the salad for at least 40 minutes to 3 hours maximum.
Before serving, taste and add salt to taste.
Serving chilled and enjoy!