A sick dick is when someone gets an erection while they are sick and proceed to have anal sex using there sick as a lubricant
Mate, I am feeling a sick dick coming on
When a girl/boy is performing oral sex and she/he then vomits on your cock.
Damn, Shelly sicked on my dick last night and got it all over my carpet which was a family heirloom.
Sick as Dick is when something is crazy good, very enjoyable or impressive. Normally used as a reply for something awesome that is mentioned to you . You would normally only say it amongst close friends, and usually followed by a shakas.
"I justbfoubd out Inhave tomorrow off"
"Sick as Dick".
Similar to "sweet dude" or "nailed it" or "whoa dude" or "that rocks".