Top definition
to underestimate the size and/or weight of ones breasts.
be careful not to underbreastimate a women's tits; they are known to suffocate small animals and children!
by Matt Huff October 06, 2011
Happy St. Patties Day!
the act of underestimating the size of your boobs when trying on clothes
Girl: "I saw this really cute shirt and it looked like it would fit perfectly, but my boobs were practically popping out. I underbreastimated big-time"
by thatsdebateable2014 June 07, 2011
Happy St. Patties Day!