George Takei. Atrocious actor who reacts to anything by looking confused or giving a shit eating grin.
Nasty person and shameless media whore too. Has milked almost 50 year old quarrels on set and his own sexuality endlessly for tabloid exposure. Feels like he should be constantly in the public eye because he had a minor role in a 60s action show. Obsessively jealous that far more talented actors get more recognition than he should be getting for saying "Aye sir!" every 3 episodes.
His comeuppance thankfully eventually came. After bitching about Shatner's acting for years he made an embarrassing tit out of himself in his Voyager episode with a performance that wouldn't be passable in a school Christmas play. Wonderful. Loathsome human being. The Paris Hilton of Star Trek. He'd do anything to become a bit more famous.
Runner up is Eric Bana as Nero but at least he has given great performances elsewhere.