Was drinking involved? It's difficult to explain rules to people who get silly when they drink.

I've not had to explain rules to people who weren't really into it in a while, but if I had to I would look to just taking a commanding tone and setting an attentive environment. Easier said than done for sure.

Don't talk until everyone is listening. State that people shouldn't: interrupt, guess rules etc. the minute those things happen.

On the teachers part be open to:

the fact that you might not be the best explainer

people learn and understand differently. Sometimes when I don't understand something, it's difficult for me to get what others don't understand.

in light of the above, don't just say the same thing over again. maybe have someone else at the table explain it

as much as I hate to admit it, there are other ways of looking at the world and at playing games

is there a simplified version you could teach first. (I recently taught Hanabi to a group and I started by playing the game with the tiles/cards facing the player, rather than the other way around. We played a quick game like that. Then we started over with the correct rule of the tiles/cards facing out. It worked really well and it really hit home the beauty and puzzle of that game.)

some people only like the social aspect of laughing and joking and maybe the game you want to play isn't really going to work. maybe it'd be better to play (gulp, i can't believe I'm saying this) Cards Against Humanity.

teaching lying is ok can be difficult

When I teach games I sometimes start backwards: I layout some of the board as if it's the end of the game and show where the scoring is, what the victory point symbol looks like, etc

Then work backwards from there: I built this train segment from Los Angeles to San Francisco using 4 orange train cards because blah blah blah

Sometimes a different game is appropriate. It might be better to start with Stone Age than Agricola. Base set Dominion than mixing 4 expansions.