The title is the key here. "Mandatory fun" names the pressure to join in, to be sociable and upbeat whether you feel like it or not. The speaker's question, "must I drink coffee / if I hate to speak," suggests a situation where coffee stands for small talk: the drink you hold while you chat. Someone who doesn't want to talk is being asked to take part anyway.
The second stanza turns strange and a little dreamlike. "Like a dry ground and the streets / full of wine" sets two opposites side by side: parched earth and streets overflowing. The fragment has no clear verb or subject, so it reads like a thought drifting in. One reading is that the speaker feels dry and empty inside while the world around them is awash in celebration. The gap between the two images makes the isolation sharper.
The mood is wry, tired, and quietly alienated. The speaker never shouts. They just ask, politely, whether they can opt out.