What does dick sneeze mean?

First, if you are not a native English speaker, be careful how you use this phrase-- it is considered crude or vulgar slang. The Urban Dictionary says it has two meanings. One refers to a small amount of ejaculate (cum) on the tip of the penis. The other is a slang expression for what the penis does at the climax of sexual intercourse. It is not a common expression, but you might hear it used by young men jokingly.