The phrase "buck off" is considered informal and often used as a way to tell someone to leave or go away. However, for a more formal tone, synonyms like "depart," "vacate," "abandon," "retreat," or "withdraw" can be used. If you want to express more urgency, you can use "get lost," "scram," or "beat it." If you want to simply ask someone to leave, you can use "excuse yourself," "make an exit," or "take a break." Whatever your intention or tone, there are many alternatives to "buck off" that can be used in various contexts.