At lunchtime, a banana, a large red grape, a carton of milk and a straw can be combined to fashion a most amusing sculpture, as follows:

1) Cut the tip off the banana.
2) Insert the straw through the cut tip, pointing down along the length of the banana. Push through until the banana is skewered on the straw, with about an inch protruding from the severed banana tip, and at least an inch protruding from somewhere along the length of the banana.
3) Blow down the straw to remove any banana detritus.
4) Cut the grape in half and attach one half this to the cut end of the banana by skewering it on the straw.
5) Take a mouthful of tasty milk. For Christ's sake, don't swallow.
6) Put mouth on non-graped end of straw and blow.
7) Sit back and enjoy your fellow students' hilarity at the sight of this facsimile of an ejaculating penis.
Don't try to be too clever and use oranges or plums for balls. Remember - less is often more, and you don't want to be accused of gilding the lily.