Some weeks, I get this question daily. It is a well-meaning question but at the same time, a meaningless one.
I am not making the parental distinction between "can I go out" and "may I go out." That drives kids nuts and it is pedantic. I wouldn't do that to you. But the truth is that anyone can sue anyone. And if I would just say "yes," that wouldn't be the answer people are looking for.
The real question is "would an attorney take my case on a contingency?" And the answer is almost always "no."
Lawyers tend to take injury cases based solely on the promise of collecting when they win because there is an insurance company on the other side. Therefore, they can evaluate the case, decide that it is a winner, and then not worry about eventually being paid. But if the defendant is an individual, unless he is personally very wealthy, an attorney can not be expected to take both risks - the risk of losing the case AND the risk of not getting paid even if he wins.
So, when you feel like saying "I want to sue that guy for defamation for $1 million!" the attorney will look past the hyperbole and ask what a jury is likely to give you, considering the loss you sustained. And if they will give you big dollars, who will write the check? We don't have debtor's prison -- there is little consequence to someone if you take a huge judgment against him and he can't pay.
"But it's the principle!"
Imagine how you would sound asking a painter to paint your house without any hope of being paid, because, in principle, it needs to be done. The painter will tell you that he can't afford to work for your principles. A lawyer is a businessman. Of course he cares about you and your case. But not enough to expend his inventory without a reasonable chance of being paid for it. And a lawyer's time is his inventory...