Crowds make a lot of people nervous. Some people simply fear the large numbers of people present; for others, it may be a heightened sense of perceived danger and unknown behavior, being left alone in the crowd, or the overload of the sensory experience of sounds and smells and even of being touched. Your character's fear of crowds may be the result of a natural aversion to groups of strangers, concerns about germs or contagion, connected to a wounding event, or tied to a fear of having a panic attack in public. For the latter, see the AGORAPHOBIA entry.

Refusing to attend crowded events, like graduations, large family reunions, and concerts
Avoiding amusement parks, zoos, fairs, and other cultural destinations
Having difficulty taking public transportation
The character having a panic attack if they're unexpectedly stuck in a crowd
Always asking to meet at smaller venues for social gatherings
The character hiding in a corner or out-of-the-way place when they encounter a crowd
Making excuses not to attend certain events
Having an escape plan in mind when a crowded venue can't be avoided
Scoping out exits upon arrival
Clinging to friends or family at large events
Scanning the crowd for points of danger
Timing attendance to coincide with off-peak times or low volumes of people 
Experiencing sensory overload in a crowd from the noise or proximity of too many people
Always leaving large events early (making a token appearance) 
Needing time to recharge and be alone after being in a crowd

The character wondering what's wrong with them