When someone or something is both fantastic and delicious or fantastic and orgasmic. Cumtastic! Can quite literally be used during any conversation, but I find I use it the most when trying to emphasize how good food is or how delicious someone looks or makes me feel.
1; Did you see how good Morgan looked today? Mmm very cumtastic!
2; I had THE best chicken and waffles the other day, they were absolutely cumtastic.
3; I love how I can just be myself with her and tell her anything. Being able to be open with someone like that is cumtastic.