What's the nastiest stuff you had to deal with? Here's my list.
1. Dictyota Algae
2. Bryopsis Algae
3. Hydrozoids
4. Caulerpa Nummularia
5. Dinoflagellate
6. Zoanthid eating nudi's
Flatworms
Red turf algae (red cotton algae in your case mike?)
Caulerpa
Geeze, and I had them all in the same tank at once -what a mother! :-[
trying to remove fish...... and then brown jelly....
At home:
Bryopsis. The single most annoying thing in my reef over time. I guess monti nudies or AEFW were annoying too, but bryopsis seems forever.
At work:
Red puffy algae.
Monti nudis
Valonia
Red turf algea
A rogue six line wrasse
Ian spending my money
Bulkhead leak
Along with the flatworms, red algae above, i'm also very annoying with
Dosing Vodka - seeing algae bloom, whit stringy strands all over my sump, skimming nasty stinky stuff, lost most of Purple algae,...and still not getting it right. Oh and testing nitrates and phosphate 
Bryan, ian (and lapsan!) tried to spend mine yesterday lol. His influence is strong and my will may break with "residual ian". Soon, I'll be a zombie and must have brains. very pretty brains!
and my sixline...he decided to jumo out of the tank a couple of weeks ago. too bad I actually liked him.
Yeah Ian is a silvered tongue person, whenever I see him he's always saying "Mike I think you should get it.." it being anything I'm looking at :D I think that's the real way he gets first pick at everything that comes in the stores, he brings in business for them 
Hey that's my job right? Who is in charge of sponsorship? haha
I believe the exact wording is "Dude, you need to get [insert expensive item here]" 
I have to know Tony, what did I almost make you buy yesterday.
Forgot what it's called, but the red poofy algae. It doesn't cling onto things very well, but that is it's benefit as it gets blown around the tank, stuck between the branches of corals, or even growing between polyps, nasty nasty stuff.
-Mike