nigger tits is used in context when one is referring to an unfortunate situation. These are not the type of tits you brag about, in fact, they are frowned upon when used in public because the two words when placed together are foul sounding. Have you ever seen a pair of nigger tits? Nothing to brag about.
Warning: Do NOT use when in a negro community as shots may be fired. They are very self concious and proud of their nigger tits.
Also, if you do not wish to add the word "tits" at the end of the phrase, simply just say "nigger."
Nigger tit can also be used as a noun when referring to an actual person.
Marisa: i fucked toure last night. i might be pregnant!
Matt: omg that kid is SUCH a nigger tit!!!!
Lindsey: Lunch will be canceled today due to lack of hustle. deal with it.
Kaylee: NO! NIGGER TITS!!