That depends on what you mean by "girls" because sometimes girls is used to describe females in general. If the men and the "girls"(women) are around the same age then it can be seen as normal, but if the girls are underage then it will most likely be perceived as perverted. Also, if the men look for an extended amount of time it can be seen as either deep interest or creepiness.
But all in all, it is normal for most people to look at anyone. If you're in the vicinity of people and have eyes that can see then you're probably going to "look" at someone. Even if it's not for a long time.
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It is natural for individuals to look at others, including those of the opposite gender. However, it is important for men (and all individuals) to be respectful and mindful of others' boundaries and to not stare or make others uncomfortable. Viewing others with respect and admiration is healthy, but objectifying or making others feel uncomfortable is not acceptable.