for me, popcorns is part of the cinema experience, as long as they don't eat it so loud until CHIK CHAK CHIK CHAk!! I'm fine with it.
For me the top 3 annoyance is:
Number 3 annoyance
Kids in cinema, without parent controlling them, running up and down, and crying. Worst experience is while watching Superman returns. We booked the 10:30pm show, thinking there shouldn't be any kids, but we were wrong! Many family bring their kids along, and some are dress up in superman costume. First they are cute to look at but the annoyance starts immediately when the movie begins. "Mommy! Where's superman?" "Daddy I wan go pee pee!" "I wan oin oin!", and there's this less than 1 year old baby crying nonstop in there.

And she only take the baby out after 15 minutes of crying non-stop.

Number 2 annoyance
Those ah beng and ah Lian's super loud ringtone, and super bright screen, it will spoil any good moments of the movies. Worst experience is while watching Ghost Riders, this ah Lian seated on front row of me but at the other far end, her phone keep on ringing loudly throughout the whole movie, some more her phone is modified with those super bright colored LEDs, so we end up with a disco lights in the cinema every time her phone rang, even after multiple loud SSHHHH!! from us she still doesn't bother to switch to silent. I almost lost my patient wanted to throw my mineral water bottle at her, luckily me wife stops me.
Number 1 annoyance
Movie commentator wannabe spoiling the story line for you. My worst experience is watching Identity, this ******* seating behind me already told his friends who is the actual killer even before the movie starts.

And While watching Starwars:III, this girl behind me keep on telling her bf, "Eh!! I think Palpatine is the bad guy lah!!! See See!!! I told you so!!!"