Internet/IM speak for a laugh and a half, meaning something is mildly amusing. Substitute for a higher fractional number if the situation calls for it (i.e. a laugh and a 0.7).
Person 1: Did you see yesterday's episode of The Daily Show? It really was a laugh and a 0.5.

Person 2 appears to be offline.
by Anouska DS October 21, 2008
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