The Trix Rabbit. You got to feel bad for a rabbit that has had to put with years of selfish kids who won't let him have his Trix because "Trix Are For Kids."
When a poll was taken to see if the Trix Rabbit should get the Trix, it was almost unanimously agreed that he should. Also, there's several commercials that seem to go out of their way to make the kids look like jerks (one having the Rabbit actually buy a box, and the kids steal it from him because "Trix are for kids")
PC in the Mac vs. PC commercials. If you're thinking of the commercials in a plot-based kind of way, he seems to have gotten progressively desperate. One can only guess that he'll end the commercial runs Lucky Channel-style.
The various rejected cleaning supplies in the Swiffer commercials.
The pea in the old Batchelor's advert (UK), made to think about the "old days on the farm, in the pod with all your friends", etc. Its own tears turn it to mush and this is supposed to make you want to eat mushy peas!
"Nobody ever pays me in gum!" Complete with "Aww..." from the other characters in the commercial.
The numerous dogs, cats, and other animals in the various animal charity commercials (the achingly sad music doesn't help). It's a toss-up as to which one makes me cry the most, but the "but I know that I am a good dog" line in the Pedigree commercial never fails to choke me up, not to mention make me wish I had a million dollars so that I could provide for all of them.
It seems like they keep on trying to make sadder and sadder commercials every-time they make one, especially the ASPCA. It hurts even more if you watch Animal Planet Heroes.
The LAMP! The little, broken-hearted lamp sitting on the curb in the IKEA commercial that everyone feels so sorry for until that Swedish asshole pops up and tells us we're being silly because it's only a lamp. Go to hell, Swedish asshole!
There isn't even anything wrong with the lamp, it still works. Why throw it away?
The Quit Smoking ad, with the young boy losing his mother in the busy public place, dear lord the poor little boy.
The stupid ad  with a rooster crowing in the middle of the night, and the lady is annoyed, and makes it leave. THEN you see it wandering in the streets, looking pitiful, crowing mournfully at a few doors, and it's raining. After a few scenes, it wanders off into the cold darkness, and the woman is smiling in her sleep, pulling those f*cking covers over her stupid, dumb head. You're supposed to think: "Good, now that woman can sleep," you end up thinking: "Poor rooster! That bitch just KICKED 'IM OUT!! He has nowehere to go!!"
The rooster shows up in the end with her coworker, who looks on in sympathy, in the cubicle next to her. Lady, you're not getting away from him that easily!
The kids in the Jell-O Temptations pudding commercials, who are jump-scared, terrified, abandoned, and forced in child slavery by their parents for eating the pudding!
The kid in that NSPCC ad. Seriously! Would YOU want to be brutally abused and burnt by your own father?!
The little salt shaker, and his friend the pepper shaker, from the Sidekicks ads. When they start crying...*sniff*
The Pepsi throwback commercial where it shows a mother fawning over her baby until the father brings the Pepsi throwback's and they start fawning over the dang sodas over their own child! Who's trying to get their attention by doing amazing things like dancing, playing guitar etc. And it just shows them paying more attention to the sodas than their own kid. "Poor baby!"
This was actually for Pepsi Max; the parents were marveling at how a soda that "contains 60% less sugar" than regular soda would taste so good and some might consider it hilarious, especially since the commercial specifically engineers it to where you the viewer concentrates first and foremost on Super Baby.
It did not help that he had a weakness for doing the same.
This little gem features an old, run-down anthropomorphic red bus who is constantly shunned by his modern white cousins, forced to sleep by a garbage container instead of a spot on the parking lot, written on ("DIRTBAG"), despised by adults and minors alike. He finally has enough of his bad luck and decides to commit suicide by hopping into a junkyard crusher. His change of heart just seconds before being crushed and a save by a butterfly make us feel all warm and fuzzy inside... And then the crusher operator flips the switch again, killing him. The narrator tells us to "show no mercy to obsolete and decrepit vehicles", while we are shown a metallic red cube circled by the aforementioned butterfly. Just to drive the point home - or perhaps to ridicule the dead protagonist further - the arrow which was stuck in the rear of the bus through the whole video is still sticking out of the cube.
The ad, fittingly titled The Sad Bus, was funded by the Polish Ministry of Interior. It advertises an online bus verification system which supposedly lets you check the technical info and condition of any bus in the country. Most viewers failed to absorb this information, since they were still emotionally reeling from the punchline.