A person who has little tolerance for the consumption of alcohol. Usually this person will make for the toilet after the consumtion of a halh-pint instead of the British standard (5 pints before breaking thwe seal). Usually found sprinting back and forth between the toilet and the bar every 15 minutes.
Check that nobber Tarquin, he's making for the trap after half a glass of Babycham. What a Shandy Pants!