When to avoid Laos depends on your personal interests and priorities. Here are some things to think about:

Climate:

Rainy season (May to October): Due to heavy rain, travel is difficult and some outdoor activities are less enjoyable. Landslides and floods can occur, especially in mountainous areas. However, lush greenery and affordability can be attractive to some people.
Dry season (November to April): Hot and sunny weather is the most popular time to visit, making it an ideal time to explore. However, you can expect higher prices and larger crowds, especially during the peak season (December to February).

Festivals and events:

Bun Pi Mai (Laos New Year): This lively festival in April includes water fights, parades, and temple rituals. It can be a fun time to experience Lao culture, but be prepared for large crowds and price hikes.
Ok Phansa: This period of religious observance lasts from July to October. Drinking and loud music are limited, but the temples are beautifully decorated and offer a glimpse into Lao Buddhist traditions.

Personal preferences:

Crowds: Avoid high season and famous tourist spots if you want quieter encounters. Consider visiting lesser-known locations such as Luang Prabang or Southern Laos.
Cots: If money is an issue, the rainy season provides reduced costs on flights and lodging. Be prepared, however, for probable travel interruptions.
Activities: Consider the things you want to do and make sure the weather and schedule are appropriate. For example, trekking might be less enjoyable during the rainy season, while festivals offer unique experiences but might clash with outdoor plans.

Finally, the best time to visit Laos is determined by your priorities and the goals of your trip. You can determine the optimum period for you by evaluating the benefits and drawbacks of each season.