My least likeable character is Herbert Birdsfoot. I had no issues with him, until July 1982 when I saw a summer rerun with Herbert's discussion about the letters M and W and their visual appearances and he turned upside down and remained that way for the remainder of the segment. It was then that I started to despise Herbert and if I was viewing Sesame clips nowadays, I would stay away from those segments, though I would have no problem with just audio.
I also hate the segment with the girl showing the number eleven upside down, too - I believe she may have also appeared (or at least looked like her) in "Alphabet Chat" - the "R" segment - as the female delivering the radiator and dropped it on Mr. Chatterly's foot.
Elmo was tolerable in his early years, but by the 1990s, Sesame Workshop overdosed on his appearances, and he was downright annoying, that could be one of the reasons why I would never watch the show these days (though not the primary reason). But at least I seemed to be more tolerable of Elmo than Herbert Birdsfoot.
And Abby Cadaby nowadays is shown too much. Too much emphasis on she and Elmo is downright overkill.