Here's a cumshot prompt that worked for me.
The 'ejaculating' 'cumshot' seems to work really well.
Prompt: 1man, naked, hairy, muscular, low angle view from directly below, standing over viewer, looking directly at viewer, legs spread, muscular hair legs, muscular hairy chest, huge erect uncut penis, shaved testicles, masturbating, ejaculating, cumshot, very sweaty, short black haircut, 45yo, mouth open in pleasure, tongue out,
Negative prompt: EasyNegative,
Steps: 35,
Sampler: DPM++ 2M SDE Heun Karras,
KSampler: dpmpp_2m_sde_gpu,
Schedule: karras,
CFG scale: 7,
Seed: 764290048,
Size: 768x1152,
VAE: Automatic,
Denoising strength: 0.9,
Clip skip: 2,
Model: Hard Muscle - Vanilla V3,
LoRA: extreme_bukkake_v0.1-pony:0.80
The 'ejaculating' 'cumshot' seems to work really well.