I wouldn't exactly say sue you, but if you dont file a return the Service will file a "subtitute" return for you, based on your income. They will assess taxes, penalties for late filing, and interest. Then they will attempt to collect what they've asessed-by garnisheing your wages and putting liens on your property, if necessary.
NOT filing is about the dumbest thing you can do. FILE, even if you can't pay. You ccan work out a plan with the Service to pay off your balances.