might as well max curse first when it is nasus vs teemo, there is pretty much no way to farm Q without taking 3+ toxic shot in the face. Wither doesn't help at all in lane, you will oom and came out losing every trade cuz on blind n poison.
Teemo bullies Nasus real hard in laning, which is what he's referring to. If you reach lategame status then sure, you'll one-shot him. Getting there is the tricky part.
Nasus has wonderful sustain to deal with the bullying, and if Teemo's in range of wither when Nasus's jungle comes, Teemo is almost guaranteed dead.
hmmm, toxic shot passive. oh you wanna wither? lemme use move quick and gtfo. oh crap, you busted ghost to get to me? lemme drop a shroom and slow you. oh damn you somehow STILL got me? well, lemme blinding dart block your q. yeah, that just happened.
yeah, it's really great to theorycraft how a fight would work how about you actually play the ****ing lane