An alternative to using expressions is Unicode characters, in this case Unicode Character 'GREATER-THAN OR EQUAL TO' (U+2265). Copying @mnel's example
.d <- data.frame(a = letters[1:6], y = 1:6)
ggplot(.d, aes(x=a,y=y)) + geom_point() +
scale_x_discrete(labels = c(letters[1:5], "u2265 80"))
Unicode is a good alternative if you have trouble remembering the complicated expression syntax or if you need linebreaks, which expressions don't allow. As a downside, whether specific Unicode characters work at all depends on your graphics device and font of choice.
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