Is the son's charity to his father, with the intention of gaining his father's pleasure, considered charity or hypocrisy?

If the charity is obligatory (Zakat (definition)), then it should not be given to parents, because their maintenance is obligatory upon the child if they are poor.

However, if it is a voluntary charity, then it is preferable to give it to parents and relatives, as Allah Almighty says: "They ask you, [O Muhammad], what they should spend. Say, 'Whatever good you spend is for parents and relatives and orphans and the needy and the traveler. And whatever good you do - indeed, Allah is Knowing of it.'" (Al-Baqarah: 215).

And pleasing one's parent with money or otherwise is not showing off; rather, it is a form of righteousness. The Prophet, peace and blessings be upon him, said: "The pleasure of the Lord is from the pleasure of the parent, and the wrath of the Lord is from the wrath of the parent." The motive for pleasing one's parent should be to attain Allah's pleasure and reward.