"Jetzt reicht es (mir)!/langt es (mir)!" ("Now that is enough"/"did it" ("for me"))
"Na, warte!" ("You just wait..." sometimes does not imply you WILL be waiting.)
"Willst (Du) Ärger/Stress?"/"Du willst wohl Stress?" (Are you looking for trouble?/You sure are looking for trouble aren't you?)
"Hast Du n' Problem?" ("Do you have a problem?") ... very offensive in certain contexts, esp because it can be interpreted as "It seems you consider ME/my group/race... a problem/unwanted/unwelcome?" or as "I seriously assume/assert you are not right in the head?!"
"Ich mach dich fertig/kaputt/platt/Krankenhaus/München/Messer" ... ("I'll break you/destroy you")... Careful, in some contexts you WILL be challenged to do so. The last three are deliberately grammatically incorrect slang ("make you hospital/Munich/knife")
"Das nimmst Du zurück, sonst." ("You take that back, or else.")
"Schnauze sonst Beule" ( (Shut up your) Snout, or (be in for a) goose egg!)
"Ich geb dir gleich...", especially combined followed by the object of a suggestion is sometimes a friendly but decisive ironic dismissal of that suggestion ("Bier trinken? Ich geb dir gleich Bier!") or of the terms used to describe something ("Wirf den alten Schrott doch weg" - "Ich geb dir gleich alten Schrott!"). Still, use that with extreme care when not familiar with it...
Disclaimer: ANY of these examples used on German speaking people can get you into a physical confrontation easily, or get you to be looked down upon as a violent/brutish/antisocial person, if your intent is misunderstood.