Drives me crazy when people create objects just to use them once, and don't even change the value of it that time. Especially when the thing goes out of scope immediately afterwards.
For example.
{
string message = "Error: user is dumb";
Textbox1.Text = message;
}
return;
WHY DO THIS. WHY. IS IT TO HASTEN MY INEVITABLE ANEURYSM. IS IT. BECAUSE THAT'S WHAT IT SEEMS LIKE. JUST SHOOT ME IN THE FACE INSTEAD. PLEASE. AT LEAST THAT'S MORE HONEST.