It is never wrong for a guy to be checking out a girl. When an attractive (of varying degree) female gets into the sight zone of a male, natural biochemical processes occur, due to the presence of a particular hormone starting with the letter T. There is thus nothing to be shameful about; as a result, nothing to hide. When checking out chicks, discretion can be exercised, but should never become a priority and when exposed, said guy should gracefully, if not proudly concede that he had been looking at a girl.
A guy should not spend more than 30 minutes contemplating if he should make a product acquisition; this can range from a gift for a fellow male friend, clothes, sneakers. This is because the level of estrogen is directly proportionate to the time spent on deciding whether to buy something. As outlined here, there are three basic outcomes. As long as the product does not fall into Class 3, then it is an acceptable choice to pick up. There is one exception to the rule, which is making a product acquisition for a specimen from the opposite (ie. female) gender. This is because females are generally confusing (as they are largely confused most of the time) in nature.
One word text replies are perfectly fine. It isn't rude to express a disinterest.
An alpha man do not attempt to create poems. He either manages to craft a nice literature piece at first try or doesn't. For budding students, you can always try the classic "Roses are red, Violets are blue". While many discard this as "lame", "stupid" and "un-original", it does have a positively corny touch to it, and if you can lace your next two lines succinctly and with some humour, then it can be pulled off.
Shoot, score, smile.