A couple TNG episodes I watched in the last few years and did not remember being all-time awful but would now nominate:
The Icarus Factor - This one isn't bad in any especially Star-Treky way, but the whole "Resentful father/son relationship healed through a violent sporting event," thing is pulled of at the absolute lowest level of TV hackwork.
Man of the People - Like Star Trek V, I could handle the sci-fi aspect of this guy's psychic powers if the real psychology that it rests on wasn't so dreadful. He's a great negotiator because his feelings don't get in way because he siphons them off to a (invariably female) victim who gets so jealous and horny that she ages and dies at dramatically accelerated speed? Yeah that makes sense. After all, the reason mediating political negotiations is hard is that it makes the negotiator super-humanly jealous and horny. Those emotions can really get in the way of the negotiations!