That isn't easy in a single regex - that isnt what they were created for, and it is a bit of a pain to implement, as you have to allow for all possible permutations yourself.
If you are doing this in C# as you say, then I would do it with two simple regexes:
Regex hyphens = new Regex("-");
Regex backslashes = new Regex(@"\\");
string inp = @"123-22-2\3";
if (hyphens.Matches(inp).Count > 1 || backslashes.Matches(inp).Count > 1)
{
}
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