Why are some men so rude ?

okay me and my boyfriend were in the pub round my area, and there's this man that I see in there every time I go in there and he has looked at me a few times.

Once he came up to me and said I looked scary but I think that was because I had purple contacts in . Anyway when me and my boyfriend were in the pub he seem to be hanging around us a lot, and said "get a room" to us. Then I noticed him grabbing girls bums and standing in front of us a lot,and being really loud, also giving my boyfriend dirty looks and then, when we went to go he stood near us laughing to his friend and said "woof woof" as we walked out. why was he being like this,hes fine usually.he hangs around with some of the people I no.