What is your best/funniest/annoying performance tuning experience? [closed]

nm: "The batch is broken"
me: "What do you mean?"
nm: "It stopped"
me: "What's the last message?"
nm: "Batch Processing Completed, total is $1234.56".
me: "Is that total correct?"
nm: "yes"
me: "So, what's the problem?"

int i;
struct { ... } a[...];

for (i = 0; i < n; i++){
    .. something involving a[i] ...
}

if (node->text_end > strlen(doc->text))
{
    throw InvalidStringRange(node->text_start, node->text_end, strlen(doc->text));
}

sub branch { system("rcs branch...") }