I remember watching a movie where a mature boy has a crush on a girl and tries to impress her. But the problem is that the girl has a dog (most probably a female dog) which creates problems that prevent them from getting together.
In one scene the couple is going to kiss but the dog licks the girl's face. The girl still tries to kiss the boy but the boy can't because he has seen the dog drinking toilet water from pot earlier before licking the girl's face (the girl doesn't notice this).
Similarly, in another scene the boy is trying to have intercourse with the girl, but the Dog got excited and licked the boy between his legs.
It's most probably an American comedy film, most likely no older than 2000, but I'm not sure about the time period. I watched it on an Indian TV channel more then 4 years ago.