sunburn on a girl's breasts (boobs)

or

sunburn on a guy's moobs (man boobs)

A portmanteau of "sunburn" and "boob"
Example 1:

I didn't reapply my sunscreen when I went to the beach, so now I have sunboob.

Example 2:

Dude #1: I don't know why Ann didn't just stay home today.
Dude #2: Yeah, her sunboob is not attractive.
by Roxanne Lalonde July 14, 2012
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