1. When Ross and Monica found out that they kissed:

2. When Ross found out that his younger sister (Monica) is dating his best friend (Chandler):

3. When Ross found out that his ex girlfriend/wife/lover (Rachel) is dating his other best friend (Joey):

4. When Ross went to get a tan and got 4 2’s on his front side instead of 2 2’s on his front and back side:

5. When Ross found out that his ex girlfriend/wife/lover (Rachel) is pregnant:

6. When Ross found out that someone at work at his turkey sandwich with a “moist maker” a.k.a the only good thing that was going on his life:

7. When Ross wanted to whiten his teeth in order to impress a date but his teeth turned out to be a little too white:

8. When Ross found that his first wife Carol is a lesbian and he gets divorced:

9. When Ross said the wrong name at the altar (he said Rachel instead of Emily) and he ends up getting divorced again:

10. When Ross and Rachel got drunk and married in Vegas after they broke up, and Ross ends up getting divorced for the third time:

Here is another description of how embarrassing Ross Geller can be just for fun: