Semen (which is the fluid containing sperm) contains about 5 calories per ejaculation, total. Assuming that all of those 5 calories derive from protein, you'd be looking at 1.25g of protein, *max*. (there are 4 cals per 1 g protein). In reality, some of those calories are coming from enzymes, sugars, etc. So you'd probably be getting a bit less than 1 g of protein.

You could easily eat that same amount of protein by consuming:

-1/5 cup of baked potato

-1/4 cup sliced avocado

-1/4 slice turkey lunchmeat

-3/4 teaspoon peanut butter

-3 almonds

If I had to choose, I'd rather eat 3 almonds than slurp down ejaculate. That's just me though.