Salsa picante is Spanish for "spicy sauce". Don Schanke uses the phrase in the episode "Dark Knight" in a sarcastic remark about Nick Knight's reaction to seeing blood. As a vampire, Nick is actually attracted rather than repelled by the sight; but he strongly objects to his condition of vampirism, and hence tries to avoid such situations. But Schanke, of course, does not know that Nick is a vampire: he thinks Nick is being squeamish.
Salsa is a Spanish, Arabic, and Italian word that can refer to any type of sauce. In American English it usually refers to a variety of spicy, tomato-based hot sauces typical of Mexican cuisine, particularly those used as dips. Having a significant proportion of tomato means that these salsas are red in colour, hence Schanke's comparison with blood.