碰杯 (pèng bēi) is more than just a celebratory clink; it's a performance of social hierarchy and respect. The act is deeply embedded in 酒桌文化 (jiǔzhuō wénhuà) - Chinese “table drinking culture.” The most critical rule involves the height of the glasses. When you 碰杯 with an elder, a senior, or someone of higher status (like a 领导 - lǐngdǎo, or boss), you must lower the rim of your glass so that it touches below the rim of their glass. This is a non-negotiable sign of deference and respect. To do otherwise is considered arrogant and disrespectful. Sometimes, both parties will try to go lower and lower in a “battle of politeness.”
You will encounter 碰杯 in almost any social setting that involves shared drinks.
It's important to note that the act of 碰杯 is often followed by the exhortation 干杯 (gānbēi), which means “dry the cup” or “bottoms up!” However, if someone says 随意 (suíyì) - “as you please” - you are only expected to take a sip.