The birthday boy's heart races as he palms the stranger's ass, feeling the taut muscles clench and release. The bus lurches, pressing their bodies together, the birthday boy's hard cock grinding against the stranger's thigh. The stranger's breath hitches, his resistance weakening as the birthday boy's fingers dip lower, tracing the crease between his cheeks. The air thickens with sweat and desire, the scent of raw, public sex permeating the bus as the birthday boy's gift becomes a hot, anonymous fuck.