Any Constructors (Badass or Standard) are a real pain for me aswell as Stalkers. Everything else is pretty easy.
Some areas that have constructors are easier than others. Like for instance in one area i can safely snipe it to death with no retaliation, while in other areas it will spam missile barrage and theres no roof over your head to protect you.
Stalkers are a pain because of the constant cloaking but they aren't as bad now as they were when i first saw them.
XBL GT: xXxwilmer007xXx | http://www.youtube.com/user/wilmer007 In CoD you USE Killstreaks, In BF you ARE the Killstreak
Hate the rabid Stalkers. Way too much health and tiny hit box when they get on you. I have used shotguns point blank into them and missing. Just total garage and takes quite a bit from the game... at least they are only in certain areas.
I don't worry about flying things due to my corrosive pistol of homing bullet awesomeness.
I run zero, so I can see stalkers and other invisible enemies when they're cloaked.
Badass constructors are a pain, but they're a sitting target. If you can find a place of shelter and snipe ... they're not a problem. Worse of a problem in open areas, but MY cloak helps a ton.
I guess my second most annoying/hated enemy are the robots that shoot rockets at you. Met them in the Ore Chasm fights. Getting killed in 1 hit isn't my idea of a fun time ... especially when they hide in the upper levels and snipe you. At least the hyperion snipers have laser sights you can track.
The badass threshers and anchormen drive me insane with their one shot hits. The threshers being even worse since you're acting like Kevin Bacon with them. For invisible enemies, aren't there also those cursed pirates or some kind of pirates in the Scarlett dlc?
For me it's the Motorcyles from Torgue. They just seem to come out of nowhere, and the way they swarm is just annoying. What can you do when you're hit from 3 different sides all at the same time? Rabid enemies aren't usually a problem for me since I use 2 shotguns...it just puts them in optimal range. I'd have to say my 2nd runner up would have to be Badass Constructors.