metric buttload n. a large but indeterminate quantity. Also metric ass-load, metric fuck-load, metric shit-load. (source: Double-Tongued Dictionary)
Further reading
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She sells seashells by the seashore. Who is the she in this tongue twister? Some claim it’s the young Mary Anning, who went on to become a famous 19th-century British paleontologist. Dubious perhaps, but the story of her rise from seaside...
I don’t know if you care about etymology, but it seems to be derived by analogy to ‘metric ton’ (1 Mg or 1000 Kg), which is about 10% larger than the ‘short ton’ of 2000 lbs. commonly referred to as ‘ton’ in the US. Therefore, a ‘metric assload’ would be even larger than a normal assload.
I read about this in “the Writer” and just had to respond. I ended up writing a blog about it. http://logikalblog.com/2009/11/17/metric-buttload/