First, let it be known that I only clicked on this thread because it was among the top most recently replied to threads on the main page, and because I saw the last response was from gunga.
Second, with regard to the OP: If you don't want to be civil, patient, and helpful to potentially new players, please do not pug low level content. Many new people are trying the game and a first party or near first party experience with someone acting the way you did may ruin it for them. Heck, I know I would definitely ruin the new player experience if they were to join my groups (I'd complete the quest before they had a chance to really play, explore, or learn anything). I shouldn't have to spell out the rest but discouraging new players is bad.
Third, the OP did make a point that I agree with: If there are requirements stated in a LFM, people should not click join if they do not meet them. However, to expect everyone to actually read (and listen to) your LFM requiements at such low levels is asking too much. You should expect extreme noobsauce if you try to pug at that level (and why would you? Do elite later. With dungeon scaling it is far far more efficient to zerg solo on N/H).
But with regard to end-game content: It's a real peeve of mine when for example I have a LFM up for shroud or TOD and we have 11 people displayed in LFM, with no cleric or FvS, where the LFM has only cleric/FvS icons selected and the LFM text states 1 spot for a healer, and someone hits join on their barb, fighter, rogue, etc.
Sometimes I'm tempted to just accept everyone and drop the group on them after. i.e. you saw I had 4 casters already and you clicked to join on your sorc, and your guildy clicked to join on his wiz? Well, alright, here's your shroud: 6 arcanes. Have fun! *pass star* *drop*
Of course, I wouldn't actually do that. The good people who were already in the group don't deserve to be punished. It's up to the group leader to screen and verify that the players they accept actually meet the specified requirements if they feel strongly about them.
Nonetheless it can be annoying and frustrating when people seemingly blindly click LFMs and subsequently ask questions like:
(i) What quest are we doing? (when the quest was stated in the LFM)
(ii) Is this for flagging or for the raid? (when there's 7+ people displayed in the party, and the precise name of the raid is selected in the LFM quest box)
(iii) Where is the quest? (when the LFM says in progress, zerging, know your way)
(iv) Do you need to flag for this? (when the LFM says abbot - selective, or "must be flagged")
(v) Can I get a teleport? (when the LFM says in progress, we're all inside, get your own ride)
Back in the day you didn't even have to specify these things in the LFM. In most cases it's completely obvious to vets simply by hovering over the LFM and seeing what the group makeup is and where everyone is located.
We joke about stuff like this and say it in our geek/noob voices when we join groups (i.e. pinch your nose and say in voice "do I need to flaaaaag for this?" or "who's on the lazer in part 7?" when zoning into a TOD). But dammit, sometimes it's no joke.