I had a similar story to Wee Stu's, though not as funny.
I was considering buying one of those ESB fresh wort kits, the stout, and putting the Burton Ale yeast in there.
"No, use the Irish Ale... Whitelabs... yeah WLP004. The sheet says to use that one."
"Yeah, this is one of my favourite yeasts I'll just grab the Burton Ale, I don't want to end up with Guinesss."
*look of shock*
"No, it won't come out right, you need to use the Irish Ale yeast mate."
"Alright, how about I get the pale ale instead... is that any good?"
"Ohhhh mate, fantastic, very good brew that one."
"Yep... whack some Muntons Gold in there too."
Luckily he didn't push the WLP001 on me, although that time he probably would have been right.
This guy also took around 7 minutes to tell me he had some Burton Ale in the fridge, on the phone. Had to call me back, then got frustrated when I didn't ask him anything else.
Another store, same company, different location, I was chasing some Centennial hops, might be called Super Cascade. The nice lady said she'd chase it up. I came in two days later to see how things were going, "We don't have any Centennial, but the closest is Pride of Ringwood, it's the same bitterness." "Ahhh, no." (yes, felt like saying great, consultation with your expert down in Sydney sure yielded some good results). I asked to see her supply list, and picked out Pacific Gem "Oh, that's weird... I would still go with POR, it's closer in bitterness to what you want." "No, I don't want my beer to taste like XXXX." and she met me with a blank look, so I just continued with "I'll take the Pacific Gem, that will be great thanks."
I have a big list of things... I'm severely tempted to open up my own HBS around these parts, just to put these stupid, stupid people out of business who seem to know nothing at all about beer. I'm definitely no guru, but it's ridiculous how incompetent some of these people are. Very tempting...