First we should make it clear that according to many Poskim, including the Mishnah Berurah, there is no obligation to get drunk on Purim. The statement in the Gemara (Megilah, 7b) that one must get drunk on Purim appears just before the equally famous statement that at a certain Purim feast, Rabah killed Rebbi Zeira. Rabbeinu Ephraim (quoted by the Ran) understands that the editors of the Gemara are telling us that because of the possible dire consequences of getting drunk, the obligation to get drunk is rejected as normative Halachah. This opinion is codified in the Shulchan Aruch by the Rema (OC 695:2) and is affirmed by the Mishnah Berurah.

Let's assume, for arguments sake, that there is an obligation to get drunk. The Shulchan Aruch (YD 240:15) states clearly that one is not obligated to obey his parents if they tell him to transgress the Halachah or refrain from performing a Mitzvah even if the Mitzvah is only Rabbinic. See Rashi (Vayikra 19:3) for the Torah source for this Halachah. So it seems straightforward that one would have to get drunk. That being said, good Midos would dictate that the son should minimize the distress he causes his parents by not performing his Mitzvah in their presence.

Kol Tuv,

Yonasan Sigler

This is not a Psak Halachah