i can't understand you if:

a) you aren't speaking english.
b) you are using directions like "the thing! get the thing! didn't you learn this in school?". actually, yes, i very likely did learn it in school, but "let's go get the thing from the thing" just doesn't help me. "you know...the THING!" also doesn't help me. let's try more specific nouns, kthx. (some you might enjoy: sock, brief, notes, binder, pen, gloves, soap...)
c) you have a very heavy spanish accent and are yelling over various machines that you would like me to do four trillion lunges across the gym and back.
d) you are the guy at tim horton's who messed up my order, TWO SUGARS TWO CREAMS HOW HARD IS IT? apparently at 4:45 am it is hard. but you know what, buddy? i'm awake to go to work and you are AT work, so ya should be awake, kthx.
e) you are the old man at mac's milk who is all like "king sized chocolate bar cheaper! buy king size!"... dear old man at mac's milk: i'm sneaking this chocolate bar on way to the gym. do not encourage me.
f) we've ever had the following conversation:
"it's not you, it's me"
ps: (it's actually you.)